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Abstract:

A toner that is excellent in low-temperature fixing property, offset
resistance, storage stability, charge rising property, charge stability
with time and pulverizability and allows for forming high-quality images
over a long period of time. The toner contains at least a binder resin, a
colorant and a charge controlling agent, wherein the charge controlling
agent contains an aromatic oxycarboxylic acid metal compound having a
trivalent or more central metal, the binder resin comprises a polyester
resin (A) having a softening point Tm (A) of 120° C. to
160° C. and a polyester resin (B) having a softening point Tm (B)
of 80° C. to less than 120° C., and at least any one of the
polyester resins (A) and (B) contains 1,2-propane diol at 65 mol % or
more in a divalent alcohol component and can be obtained by condensation
polymerizing an alcohol component substantially composed of only an
aliphatic alcohol with a carboxylic acid component.

Claims:

1. A toner, comprising:a binder resin,a colorant, anda charge controlling
agent,wherein the charge controlling agent comprises an aromatic
oxycarboxylic acid metal compound having a trivalent or more central
metal, the binder resin comprises a polyester resin (A) having a
softening point Tm (A) of 120.degree. C. to 160.degree. C. and a
polyester resin (B) having a softening point Tm (B) of 80.degree. C. to
less than 120.degree. C., and at least any one of the polyester resins
(A) and (B) contains 1,2-propane diol at a content of 65 mol % or more in
a divalent alcohol component and can be obtained by condensation
polymerizing an alcohol component substantially composed of only an
aliphatic alcohol with a carboxylic acid component.

2. The toner according to claim 1, wherein the aromatic oxycarboxylic acid
metal compound is represented by the following General Formula (1),where,
R1 represents any one of a carbon atom, a methine group and a
methylene group, the methine group and the methylene group may
respectively contain a hetero atom selected from N, S and P; "Y"
represents a ring structure linked by saturated bond(s) or unsaturated
bond(s); R2 and R3 respectively represent a hydrogen atom, a
halogen atom, a hydroxyl group, a nitro group, a nitroso group, a
sulfonyl group, a cyano group, an alkyl group, alkenyl group, an alkoxy
group, an aryl group, an aryloxy group, an aralkyl group, an aralkyloxy
group, an amino group, a carboxyl group and a carbonyl group, and when
"o" and "p" are respectively an integer of 1 or more, R2 and R3
may be the same to each other or different from each other, and R2
and R3 may be further substituted by a substituent group; R4
represents any one of a hydrogen atom and an alkyl group; "1" is zero or
an integer of 3 to 12; "m" is an integer of 1 to 20; "n" is zero or an
integer of 1 to 20; "o" is zero or an integer of 1 to 4; "p" is zero or
an integer of 1 to 4; "q" is zero or an integer of 1 to 3; "r" is an
integer of 1 to 20; "s" is zero or an integer of 1 to 20; and "M" is a
trivalent or more central metal.

3. The toner according to claim 1, wherein the central metal is iron.

4. The toner according to claim 1, wherein the central metal is zirconium.

5. The toner according to claim 1, wherein the content of the aliphatic
alcohol in the alcohol component is 90 mol % or more.

6. The toner according to claim 1, wherein the alcohol component contained
in at least any one of the polyester resins (A) and (B) further comprises
glycerine.

7. The toner according to claim 1, wherein the alcohol component contained
in the polyester resin (A) further comprises 1,3-propane diol.

8. The toner according to claim 1, wherein the carboxylic acid component
contained in at least any one of the polyester resins (A) and (B)
comprises an aliphatic dicarboxylic acid compound having 2 to 4 carbon
atoms.

9. The toner according to claim 1, wherein the carboxylic acid component
contained in at least any one of the polyester resins (A) and (B)
comprises a purified rosin.

10. The toner according to claim 1, wherein the mass ratio of the
polyester resin (A) to the polyester resin (B) [(A)/(B)] is 1/9 to 9/1.

11. The toner according to claim 1, wherein the difference in softening
point (Tm) between the polyester resin (A) and the polyester resin (B)
[Tm (A)-Tm (B)] is 10.degree. C. or more.

12. An image forming apparatus, comprising:a latent electrostatic image
bearing member,a charging unit configured to charge the surface of the
latent electrostatic image bearing member,an exposing unit configured to
expose the charged surface of the latent electrostatic image bearing
member to form a latent electrostatic image,a developing unit configured
to develop the latent electrostatic image using a toner to form a visible
image,a transfer unit configured to transfer the visible image onto a
recording medium, anda fixing unit configured to fix the transferred
image on the recording medium,wherein the toner comprises a binder resin,
a colorant and a charge controlling agent,wherein the charge controlling
agent comprises an aromatic oxycarboxylic acid metal compound having a
trivalent or more central metal, the binder resin comprises a polyester
resin (A) having a softening point Tm (A) of 120.degree. C. to
160.degree. C. and a polyester resin (B) having a softening point Tm (B)
of 80.degree. C. to less than 120.degree. C., and at least any one of the
polyester resins (A) and (B) contains 1,2-propane diol at a content of 65
mol % or more in a divalent alcohol component and can be obtained by
condensation polymerizing an alcohol component substantially composed of
only an aliphatic alcohol with a carboxylic acid component.

13. The image forming apparatus according to claim 12, wherein the
charging unit is configured to charge the surface of the latent
electrostatic image bearing member in non-contact with the latent
electrostatic image bearing member.

14. The image forming apparatus according to claim 12, wherein the
charging unit is configured to charge the surface of the latent
electrostatic image bearing member in contact with the latent
electrostatic image bearing member.

15. The image forming apparatus according to claim 12, wherein the
developing unit comprises a magnetic field generating unit fixed inside
the developing unit and a developer carrier that carries a two-component
developer composed of a magnetic carrier and the toner on the surface of
the developing unit, and the developing unit is rotatable.

16. The image forming apparatus according to claim 12, wherein the
developing unit comprises a developer carrier to which the toner is
supplied and a layer thickness controlling member that forms a toner-thin
layer on the surface thereof

17. The image forming apparatus according to claim 12, wherein a plurality
of image forming sections are arranged, each of which comprises at least
a latent electrostatic image bearing member, a charging unit, a
developing unit and a transfer unit, and the transfer unit is configured
to sequentially transfer visual images formed on each of the respective
latent electrostatic image bearing members onto a recording medium whose
surface moves so as to pass a transfer position that faces the respective
latent electrostatic image bearing members.

18. The image forming apparatus according to claim 12, wherein the
transfer unit comprises an intermediate transfer member on which a
visible image formed on the latent electrostatic image bearing member is
primarily transferred and a secondary transfer unit configured to
secondarily transfer the visible image carried by the intermediate
transfer member onto a recording medium.

19. An image forming method, comprising:charging the surface of a latent
electrostatic image bearing member,exposing the charged surface of the
latent electrostatic image bearing member to form a latent electrostatic
image,developing the latent electrostatic image using a toner to form a
visible image,transferring the visible image onto a recording medium,
andfixing the transferred image on the recording medium,wherein the toner
comprises a binder resin, a colorant and a charge controlling
agent,wherein the charge controlling agent comprises an aromatic
oxycarboxylic acid metal compound having a trivalent or more central
metal, the binder resin comprises a polyester resin (A) having a
softening point Tm (A) of 120.degree. C. to 160.degree. C. and a
polyester resin (B) having a softening point Tm (B) of 80.degree. C. to
less than 120.degree. C., and at least any one of the polyester resins
(A) and (B) contains 1,2-propane diol at a content of 65 mol % or more in
a divalent alcohol component and can be obtained by condensation
polymerizing an alcohol component substantially composed of only an
aliphatic alcohol with a carboxylic acid component.

20. A process cartridge detachably mountable to an image forming apparatus
main body, comprising:a latent electrostatic image bearing member, anda
developing unit configured to develop a latent electrostatic image formed
on the latent electrostatic image bearing member using a toner to form a
visible image,wherein the toner comprises a binder resin, a colorant and
a charge controlling agent,wherein the charge controlling agent comprises
an aromatic oxycarboxylic acid metal compound having a trivalent or more
central metal, the binder resin comprises a polyester resin (A) having a
softening point Tm (A) of 120.degree. C. to 160.degree. C. and a
polyester resin (B) having a softening point Tm (B) of 80.degree. C. to
less than 120.degree. C., and at least any one of the polyester resins
(A) and (B) contains 1,2-propane diol at a content of 65 mol % or more in
a divalent alcohol component and can be obtained by condensation
polymerizing an alcohol component substantially composed of only an
aliphatic alcohol with a carboxylic acid component.

Description:

BACKGROUND OF THE INVENTION

[0001]1. Field of the Invention

[0002]The present invention relates to a toner used for
electrophotographic image formation such as for copiers, electrostatic
printing, printers, facsimiles, electrostatic recording and the like, and
also relates to an image forming apparatus using the toner, an image
forming method using the toner, and a process cartridge using the toner.

[0003]2. Description of the Related Art

[0004]Conventionally, various methods of electrophotographic image
formation have been known in the art. Generally, the surface of a latent
electrostatic image bearing member (hereinafter, may be referred to as
"photoconductor", "electrophotographic photoconductor" or "image bearing
member") is charged and the charged surface of the latent electrostatic
image bearing member is exposed to form a latent electrostatic image.
Next, the latent electrostatic image is developed to form a visible image
on the latent electrostatic image bearing member. The visible image is
directly transferred onto a recording medium or transferred via an
intermediate transfer member onto a recording medium, and the transferred
image is fixed by heating and/or pressurizing the transferred image,
thereby obtaining a recorded material with an image formed on the
recording medium. Then, a residual toner remaining on the surface of the
latent electrostatic image bearing member after transfer of the visible
image is removed by a known method using a cleaning blade, cleaning
brush, cleaning roller or the like.

[0005]For a full-color image forming apparatus utilizing such an
electrophotographic technique, typically, there are two methods known in
the art. One method is called a single method (or single drum method). In
the single method, one latent electrostatic image bearing member is
mounted inside an image forming apparatus, and four developing units each
corresponding to each four colors of cyan, magenta, yellow and black are
mounted inside the image forming apparatus. In such a single method, four
color visible images are formed on the latent electrostatic image bearing
member or a recording medium. The single method enables to share a single
charging unit, a single exposing unit, a single transfer unit, a single
cleaning unit and the like that are arranged around a latent
electrostatic image bearing member, and the single method allows an image
forming apparatus to be designed compact at low-production cost, as
compared to a tandem method, which will be described hereinafter.

[0006]Another method is called a tandem method (or tandem-drum method). In
the tandem method, a plurality of latent electrostatic image bearing
members are mounted inside an image forming apparatus (see Japanese
Patent Application Laid-Open (JP-A) No. 5-341617). Typically, one
charging unit, one developing unit, one transfer unit and one cleaning
unit are arranged for one latent electrostatic image bearing member, all
of them constitute one image forming constitutional element, and a
plurality of the image forming constitutional elements (typically, four
image forming constitutional elements) are mounted inside an image
forming apparatus. In the tandem method, a one-color visible image is
formed using one image forming constitutional element, and four-color
visible images are sequentially transferred onto a recording medium to
thereby form a full-color image. The tandem method enables to produce
respective color-visible images by parallel processing, and thus it
allows for high-speed image formation. Specifically, the tandem method
requires only about one-fourth of the image forming processing time
required for the single method and can form an image at a printing speed
four-times as high as the printing speed of the single method. Further,
the tandem method can virtually increase the durability of respective
units such as a latent electrostatic image bearing member in an image
forming constitutional element. This is because the tandem method
requires just only one operation to perform the above-noted steps using
one latent electrostatic image bearing member, in contrast to the single
method, in which one latent electrostatic image bearing member goes
through four times of respective steps of charging, exposing, developing
and transferring to form a full-color image.

[0007]However, in the tandem method, it is necessary to arrange a
plurality of image forming sections, and thus the method has a
disadvantage in that there is a need to increase the size of the main
body of an image forming apparatus, resulting in high-production cost.

[0008]To solve the aforementioned problem, there is a method of making a
latent electrostatic image bearing member have a smaller diameter and
down-sized respective units arranged around the latent electrostatic
image bearing member, thereby reducing one image forming constitutional
element in size. As a result, it is possible to obtain not only an effect
of downsizing of the main body of an image forming apparatus but also an
effect of reducing material cost, and overall cost-cutting of such an
image forming apparatus has proceeded in some degree. With achievement of
such compact and down-sized image forming apparatuses, the following new
problems are introduced. Respective units to be mounted to an image
forming constitutional element must be made to achieve high-performance
and to achieve highly increased stability.

[0009]Further, recently, demands in the market for energy-saving and
high-speed performance in image forming apparatuses, such as printers,
copiers and facsimiles, have become strong. To achieve such
high-performance in an image forming apparatus, it is important to
improve thermal efficiency of a fixing unit.

[0010]Generally, in an image forming apparatus, an unfixed toner image is
formed on a recording medium such as a recording sheet, printing paper,
photosensitive paper and electrostatic printing paper through an image
formation process such as electrophotographic recording, electrostatic
recording and magnetic recording by an indirect transfer or direct
transfer method. As a fixing unit to fix such an unfixed toner image, for
example, contact heating methods such as heat roller method, film heating
method and electromagnetic induction heating method are widely employed.

[0011]The heat roller type fixing unit is basically composed of a pair of
rotation rollers of a fixing roller which has a thermal source, such as a
halogen lamp, inside thereof to thermally control the temperature to a
predetermined value and a pressurizing roller that is pressed against the
fixing roller to make contact therewith. A recording medium is inserted
into a contact portion (so-called nip portion) of the pair of rotation
rollers to convey the recording medium, and an unfixed toner image is
fused and fixed on the recording medium by heat and pressure from the
fixing roller and the pressurizing roller.

[0012]Film heating type fixing units have been proposed, for example, in
Japanese Patent Application Laid-Open (JP-A) Nos. 63-313182 and 1-263679.
Such a film heating type fixing unit is configured to supply heat via a
fixing thin film having heat resistance from a heater which is fixed to
and supported with a supporting member by making a recording medium
closely contact with the heater via the fixing thin film while sliding
the fixing thin film against the heater and moving.

[0013]For the heater, for example, a ceramic heater having a heat
resistant layer formed on a ceramic substrate made of alumina, aluminum
nitride or the like, which has properties such as heat resistance,
insulation and excellent thermal conductance, is used. In such a fixing
unit, a fixing film which is thin and is of low heat capacity can be
used, and it has higher heat transfer efficiency than the above-noted
heat roller type fixing unit, enables to shorten warm-up time and allows
for quick starting and energy-saving.

[0014]For the electromagnetic induction heating type fixing unit, for
example, a technique of making a heater having a magnetic metal member
electromagnetically induce and generate heat by generating Joule heat
using an eddy current generated from an AC magnetic field in the magnetic
metal member has been proposed (see Japanese Patent Application Laid-Open
(JP-A) No. 8-22206).

[0015]In such an electromagnetic induction heating type fixing unit, to
wrap around a visible image and to uniformly heat and fuse the visible
image, a film having a rubber elastic layer on the surface thereof is
placed in between a heater and a recording medium. When the rubber
elastic layer is formed with a silicone rubber or the like, the heat
responsiveness becomes poor due to its low thermal conductance, resulting
in an extremely large temperature difference between the inner surface of
the film heated from the heater and the outer surface of the film being
contact with a toner. When a toner adhesion amount is large, the belt
surface temperature is rapidly lowered, sufficient fixing ability cannot
be ensured, and consequently so-called cold offset may occur.

[0016]Further, a fixing unit used in an electrophotographic image forming
apparatus is required to have toner-releasing property (hereinafter, may
be referred to as "offset resistance") to a heating member. Such offset
resistance can be improved by making a releasing agent exist on the
surface of the toner, however, when a predetermined toner is used or a
used toner is reused, the amount of a releasing agent existing on the
toner surface is reduced and the offset resistance of the toner may
degrade.

[0017]Further, with achievement of an image forming apparatus allowing
high-speed performance and energy saving, there is a need to use a toner
that is excellent in low-temperature fixing property. In the meanwhile, a
toner having offset resistance and storage stability (blocking
resistance) conflicting with the low-temperature fixing property is
required. To respond to the need, a toner using an aromatic polyester
resin is proposed, however, the toner has a shortcoming of being poor in
pulverizability in production process. To address the shortcoming, a
method is proposed in which a low-molecular weight polyester using an
aliphatic alcohol which is excellent in pulverizability as a monomer and
a high-molecular weight polyester are blended. (see Japanese Patent
Application Laid-Open (JP-A) No. 2002-287427). However, a low-molecular
weight polyester using an aliphatic alcohol has a low glass transition
temperature because of its structure, the storage stability of the toner
degrades, and thus it is difficult to keep both offset resistance and
storage stability at a high level. Furthermore, with speeding up of
developing in recent years, a toner is required to have a high-charge
rising property, however, the toner does not have sufficient charge
rising property.

[0018]To improve charge rising property of a toner, adding a charge
controlling agent in a toner is the most common method. For typical
charge controlling agents, chelate compounds containing salicylic acid,
oxysalicylic acid or the like as a ligand are exemplified. Metal complex
salts of such salicylic acid derivatives are proposed in Japanese Patent
Application Laid-Open (JP-A) Nos. 62-145255, 55-42752 and the like,
however, in these proposals, the controlling agents respectively contain
heavy metal such as Cr and Co, and accordingly it is unfavorable to use
them in terms of environmental safety.

[0019]Then, in consideration of environmental safety, there have been a
number of salicylic acid derivatives proposed which have Fe as a central
metal and contains no heavy metals such as Cr and Co therein. For
example, Japanese Patent Application Laid-Open (JP-A) No. 1-309072
discloses an effect of limiting controlling agents to be used to metal
complexes of salicylic acid derivatives having a carboxyl group or a
sulfoxylic group as a substituent group. Japanese Patent Application
Laid-Open (JP-A) No. 9-325520 discloses an effect of using only a
combination of specific resins and a combination of iron complexes of
salicylic acid as ligands. Further, Japanese Patent Application Laid-Open
(JP-A) Nos. 7-230188 and 10-10785 respectively disclose an effect of
using a combination of iron complexes of specific resins and
oxycarboxylic acid as ligands. However, the proposed techniques exert
their effects only when limiting it to a combination of a specific resin
and an iron complex of salicylic acid derivative.

[0020]Further, Japanese Patent Application Laid-Open (JP-A) No.
2001-343787 discloses an effect of using a combination of a non-linear
polyester resin which specifies a hydroxy value and a metal complex of
salicylic acid derivative, however, when using a polyester resin in which
an aliphatic alcohol that is not particularly limited is used as a
monomer, the charge amount distribution becomes wide to cause a variation
in charge amount among toner particles. Furthermore, because of the
structure of the monomer, the mechanical strength of the toner is weak,
and the surface of the toner deteriorates by being stirred and shared in
a developing device, and the charge amount of toner is significantly
reduced with stirring time, which adversely affects quality of image,
consequently.

[0021]Accordingly, the present situation is that it is desired to
immediately provide a toner which is excellent in all the properties of
low-temperature fixing property, offset resistance, storage stability,
charge rising property, charge stability with time and pulverizability
and allows for forming high-quality images over a long period of time, an
image forming apparatus using the toner, an image forming method using
toner as well as a process cartridge using the toner.

BRIEF SUMMARY OF THE INVENTION

[0022]The present invention aims to solve the conventional problems and
achieve the following objects. Specifically, the present invention aims
to provide a toner which is excellent in all the properties of
low-temperature fixing property, offset resistance, storage stability,
charge rising property, charge stability with time and pulverizability
and allows for forming high-quality images over a long period of time,
and to provide an image forming apparatus, an image forming method and a
process cartridge each of which uses the toner and allows for forming
extremely high-quality images over a long period of time without causing
color tone change and abnormal images such as reduction in image density
and background smear.

[0023]The means to solve the aforementioned problems are as follows.

[0024]1> A toner containing a binder resin, a colorant, and a charge
controlling agent, wherein the charge controlling agent contains an
aromatic oxycarboxylic acid metal compound having a trivalent or more
central metal, the binder resin contains a polyester resin (A) having a
softening point Tm (A) of 120° C. to 160° C. and a
polyester resin (B) having a softening point Tm (B) of 80° C. to
less than 120° C., and at least any one of the polyester resins
(A) and (B) contains 1,2-propane diol at a content of 65 mol % or more in
a divalent alcohol component and can be obtained by condensation
polymerizing an alcohol component substantially composed of only an
aliphatic alcohol with a carboxylic acid component.

[0025]2> The toner according to the item <1>, wherein the
aromatic oxycarboxylic acid metal compound is represented by the
following General Formula (1),

[0026]where, R1 represents any one of a carbon atom, a methine group
and a methylene group, the methine group and the methylene group may
respectively contain a hetero atom selected from N, S and P; "Y"
represents a ring structure linked by saturated bond(s) or unsaturated
bond(s); R2 and R3 respectively represent a hydrogen atom, a
halogen atom, a hydroxyl group, a nitro group, a nitroso group, a
sulfonyl group, a cyano group, an alkyl group, alkenyl group, an alkoxy
group, an aryl group, an aryloxy group, an aralkyl group, an aralkyloxy
group, an amino group, a carboxyl group and a carbonyl group, and when
"o" and "p" are respectively an integer of 1 or more, R2 and R3
may be the same to each other or different from each other, and R2
and R3 may be further substituted by a substituent group; R4
represents any one of a hydrogen atom and an alkyl group; "1" is zero or
an integer of 3 to 12; "m" is an integer of 1 to 20; "n" is zero or an
integer of 1 to 20; "o" is zero or an integer of 1 to 4; "p" is zero or
an integer of 1 to 4; "q" is zero or an integer of 1 to 3; "r" is an
integer of 1 to 20; "s" is zero or an integer of 1 to 20; and "M" is a
trivalent or more central metal.

[0027]3> The toner according to any one of the items <1> to
<2>, wherein the central metal is iron.

[0028]4> The toner according to any one of the items <1> to
<2>, wherein the central metal is zirconium.

[0029]5> The toner according to any one of the items <1> to
<4>, wherein the content of the aliphatic alcohol in the alcohol
component is 90 mol % or more.

[0030]6> The toner according to any one of the items <1> to
<5>, wherein the alcohol component contained in at least any one of
the polyester resins (A) and (B) further contains glycerine.

[0031]7> The toner according to any one of the items <1> to
<6>, wherein the alcohol component contained in the polyester resin
(A) further contains 1,3-propane diol.

[0032]8> The toner according to any one of the items <1> to
<7>, wherein the carboxylic acid component contained in at least
any one of the polyester resins (A) and (B) contains an aliphatic
dicarboxylic acid compound having 2 to 4 carbon atoms.

[0033]9> The toner according to any one of the items <1> to
<8>, wherein the carboxylic acid component contained in at least
any one of the polyester resins (A) and (B) contains a purified rosin.

[0034]10> The toner according to any one of the items <1> to
<9>, wherein the mass ratio of the polyester resin (A) to the
polyester resin (B) [(A)/(B)] is 1/9 to 9/1.

[0035]11> The toner according to any one of the items <1> to
<10>, wherein the difference in softening point (Tm) between the
polyester resin (A) and the polyester resin (B) [Tm (A)-Tm (B)] is
10° C. or more.

[0036]12> The toner according to any one of the items <1> to
<11>, wherein the weight average particle diameter of the toner is
3 μm to 10 μm.

[0037]13> A developer containing a toner, wherein the toner contains a
binder resin, a colorant and a charge controlling agent; the charge
controlling agent contains an aromatic oxycarboxylic acid metal compound
having a trivalent or more central metal, the binder resin contains a
polyester resin (A) having a softening point Tm (A) of 120° C. to
160° C. and a polyester resin (B) having a softening point Tm (B)
of 80° C. to less than 120° C., and at least any one of the
polyester resins (A) and (B) contains 1,2-propane diol at a content of 65
mol % or more in a divalent alcohol component and can be obtained by
condensation polymerizing an alcohol component substantially composed of
only an aliphatic alcohol with a carboxylic acid component.

[0038]14> A toner container filled with a toner, wherein the toner is a
toner according to any one of the items <1> to <12>.

[0039]15> An image forming apparatus having a latent electrostatic
image bearing member, a charging unit configured to charge the surface of
the latent electrostatic image bearing member, an exposing unit
configured to expose the charged surface of the latent electrostatic
image bearing member to form a latent electrostatic image, a developing
unit configured to develop the latent electrostatic image using a toner
to form a visible image, a transfer unit configured to transfer the
visible image onto a recording medium, and a fixing unit configured to
fix the transferred image on the recording medium, wherein the toner is a
toner according to any one of the items <1> to <12>.

[0040]16> The image forming apparatus according to the item
s<15>, wherein the charging unit is configured to charge the
surface of the latent electrostatic image bearing member in non-contact
with the latent electrostatic image bearing member.

[0041]17> The image forming apparatus according to the item <15>,
wherein the charging unit is configured to charge the surface of the
latent electrostatic image bearing member in contact with the latent
electrostatic image bearing member.

[0042]18> The image forming apparatus according to any one of the items
<15> to <17>, wherein the developing unit has a magnetic
field generating unit fixed inside the developing unit and a developer
carrier that carries a two-component developer composed of a magnetic
carrier and the toner on the surface of the developing unit, and the
developing unit is rotatable.

[0043]19> The image forming apparatus according to any one of the items
<15> to <17>, wherein the developing unit has a developer
carrier to which the toner is supplied and a layer thickness controlling
member that forms a toner-thin layer on the surface thereof.

[0044]20> The image forming apparatus according to any one of the items
<15> to <19>, wherein the transfer unit is configured to
transfer a visible image formed on the latent electrostatic image bearing
member onto a recording medium.

[0045]21> The image forming apparatus according to any one of the items
<15> to <20>, wherein a plurality of image forming sections
are arranged, each of which has at least a latent electrostatic image
bearing member, a charging unit, a developing unit and a transfer unit,
and the transfer unit is configured to sequentially transfer visual
images formed on each of the respective latent electrostatic image
bearing members onto a recording medium whose surface moves so as to pass
a transfer position that faces the respective latent electrostatic image
bearing members.

[0046]22> The image forming apparatus according to any one of the items
<15> to <19>, wherein the transfer unit has an intermediate
transfer member on which a visible image formed on the latent
electrostatic image bearing member is primarily transferred and a
secondary transfer unit configured to secondarily transfer the visible
image carried by the intermediate transfer member onto a recording
medium.

[0047]23> The image forming apparatus according to any one of the items
<15> to <22>, further having a cleaning unit, wherein the
cleaning unit has a cleaning blade that makes contact with the surface of
the latent electrostatic image bearing member.

[0048]24> The image forming apparatus according to any one of the items
<15> to <22>, wherein the developing unit has a developer
carrier that makes contact with the surface of the latent electrostatic
image bearing member and is configured to develop a latent electrostatic
image formed on the latent electrostatic image bearing member and collect
a residual toner remaining on the surface of the latent electrostatic
image bearing member.

[0049]25> The image forming apparatus according to any one of the items
<15> to <24>, wherein the fixing unit has at least any one of
a roller and a belt and is configured to fix a transferred image on a
recording medium by heating the transferred image from the surface of at
least any one of the roller and the belt that does not make contact with
the toner and pressurizing the transferred image on the recording medium.

[0050]26> The image forming apparatus according to any one of the items
<15> to <24>, wherein the fixing unit has at least any one of
a roller and a belt and is configured to fix a transferred image on a
recording medium by heating the transferred image from the surface of at
least any one of the roller and the belt that makes contact with the
toner and pressurizing the transferred image on the recording medium.

[0051]27> An image forming method including charging the surface of a
latent electrostatic image bearing member, exposing the charged surface
of the latent electrostatic image bearing member to form a latent
electrostatic image, developing the latent electrostatic image using a
toner to form a visible image, transferring the visible image onto a
recording medium, and fixing the transferred image on the recording
medium, wherein the toner is a toner according to any one of the items
<1> to <12>.

[0052]28> The image forming method according to the item <27>,
wherein the surface of the latent electrostatic image bearing member is
charged in non-contact with the latent electrostatic image bearing
member.

[0053]29> The image forming method according to the item <27>,
wherein the surface of the latent electrostatic image bearing member is
charged in contact with the latent electrostatic image bearing member.

[0054]30> The image forming method according to any one of the items
<27> to <29>, wherein the latent electrostatic image is
developed using a rotatable developing unit that has a magnetic field
generating unit fixed inside the developing unit and a developer carrier
that carries a two-component developer composed of a magnetic carrier and
the toner on the surface of the developing unit.

[0055]31> The image forming method according to any one of the items
<27> to <29>, wherein the latent electrostatic image is
developed using a developing unit that has a developer carrier to which
the toner is supplied and a layer thickness controlling member that forms
a toner-thin layer on the surface thereof.

[0056]32> The image forming method according to any one of the items
<27> to <31>, wherein in the transferring, a visible image
formed on the latent electrostatic image bearing member is transferred
onto a recording medium.

[0057]33> The image forming method according to any one of the items
<27> to <32>, wherein an image is formed using a plurality of
image forming sections are arranged, each of which has at least a latent
electrostatic image bearing member, a charging unit, a developing unit
and a transfer unit, and the transfer unit is configured to sequentially
transfer visual images formed on each of the respective latent
electrostatic image bearing members onto a recording medium whose surface
moves so as to pass a transfer position that faces the respective latent
electrostatic image bearing members.

[0058]34> The image forming method according to any one of the items
<27> to <31>, wherein in the transferring, a transfer unit is
used which has an intermediate transfer member on which a visible image
formed on the latent electrostatic image bearing member is primarily
transferred and a secondary transfer unit configured to secondarily
transfer the visible image carried by the intermediate transfer member
onto a recording medium.

[0059]35> The image forming method according to any one of the items
<27> to <34>, further including cleaning the surface of the
latent electrostatic image bearing member using a cleaning blade that
makes contact with the surface of the latent electrostatic image bearing
member.

[0060]36> The image forming method according to any one of the items
<27> to <34>, wherein in the developing, a developing unit is
used which has a developer carrier that makes contact with the surface of
the latent electrostatic image bearing member and is configured to
develop a latent electrostatic image formed on the latent electrostatic
image bearing member and collect a residual toner remaining on the
surface of the latent electrostatic image bearing member.

[0061]37> The image forming method according to any one of the items
<27> to <36>, wherein in the fixing, a transferred image is
fixed on a recording medium using a fixing unit that has at least any one
of a roller and a belt and is configured to fix a transferred image on a
recording medium by heating the transferred image from the surface of at
least any one of the roller and the belt that does not make contact with
the toner and pressurizing the transferred image on the recording medium.

[0062]38> The image forming method according to any one of the items
<27> to <36>, wherein in the fixing, a transferred image is
fixed on a recording medium using a fixing unit that has at least any one
of a roller and a belt and is configured to fix a transferred image on a
recording medium by heating the transferred image from the surface of at
least any one of the roller and the belt that makes contact with the
toner and pressurizing the transferred image on the recording medium.

[0063]39> A process cartridge detachably mountable to an image forming
apparatus main body including a latent electrostatic image bearing
member, and a developing unit configured to develop a latent
electrostatic image formed on the latent electrostatic image bearing
member using a toner to form a visible image, wherein the toner is a
toner according to any one of the items <1> to <12>.

[0064]The toner of the present invention contains at least a binder resin,
a colorant and a charge controlling agent, wherein the charge controlling
agent contains an aromatic oxycarboxylic acid metal compound having a
trivalent or more central metal, the binder resin contains a polyester
resin (A) having a softening point Tm (A) of 120° C. to
160° C. and a polyester resin (B) having a softening point Tm (B)
of 80° C. to less than 120° C., and at least any one of the
polyester resins (A) and (B) contains 1,2-propane diol at a content of 65
mol % or more in a divalent alcohol component and can be obtained by
condensation polymerizing an alcohol component substantially composed of
only an aliphatic alcohol with a carboxylic acid component. In the toner
of the present invention, the polyester resin (A) having a high-softening
point contributes to enhancement of offset resistance, the polyester
resin (B) having a low-softening point contributes to enhancement of
low-temperature fixing property, and the use of a combination thereof is
effective to obtain both of the low-temperature fixing property and the
offset resistance. The 1,2-propane diol which is a branched-chain alcohol
having 3 carbon atoms is more effective in enhancing the low-temperature
fixing property of the toner while maintaining its offset resistance than
use of an alcohol having 2 or less carbon atoms and allows for fixing an
image at an extremely low temperature and improving storage stability of
the toner. The aromatic oxycarboxylic acid metal compound having a
trivalent or more central metal can be extremely excellently dispersed in
a polyester resin containing 1,2-propane diol as an alcohol component and
is excellent in charge rising property. Then, by synergistic action of
these compounds, it is possible to produce a toner which is excellent in
all the properties of low-temperature fixing property, offset resistance,
storage stability, charge rising property, charge stability with time and
pulverizability and also possible to form a high-quality image.

[0065]The developer of the present invention contains the toner of the
present invention. Therefore, when an image is formed through an
electrophotographic process using the developer, a high-quality image can
be obtained because the toner is excellent in all the properties of
low-temperature fixing property, offset resistance, storage stability,
charge rising property, charge stability with time and pulverizability.

[0066]A toner container according to the present invention houses the
toner of the present invention therein. Therefore, when an image formed
through an electrophotographic process using the toner housed in the
toner container, a highly fine image can be favorably formed because the
toner is excellent in all the properties of low-temperature fixing
property, offset resistance, storage stability, charge rising property,
charge stability with time and pulverizability.

[0067]The image forming apparatus of the present invention has at least a
latent electrostatic image bearing member, a charging unit configured to
charge the surface of the latent electrostatic image bearing member, an
exposing unit configured to expose the charged surface of the latent
electrostatic image bearing member to form a latent electrostatic image,
a developing unit configured to develop the latent electrostatic image
using a toner to form a visible image, a transfer unit configured to
transfer the visible image onto a recording medium and a fixing unit
configured to fix the transferred image on the recording medium, in which
for the toner, the toner of the present invention is used.

[0068]In the image forming apparatus of the present invention, the
charging unit uniformly charges the surface of the latent electrostatic
image bearing member. The exposing unit exposes the surface of the latent
electrostatic image bearing member to form a latent electrostatic image.
The developing unit develops the latent electrostatic image formed on the
latent electrostatic image bearing member using a toner to form a visible
image. The transfer unit transfers the visible image onto a recording
medium. The fixing unit fixes a transferred image on the recording
medium. In the image formation process, since the toner of the present
invention is used, it is possible to form an extremely high-quality image
over a long period of time without substantially causing a change in
color tone and abnormal images such as reduction in image density and
background smear.

[0069]The image forming method of the present invention includes at least
charging the surface of a latent electrostatic image bearing member,
exposing the charged surface of the latent electrostatic image bearing
member to form a latent electrostatic image, developing the latent
electrostatic image using a toner to form a visible image, transferring
the visible image onto a recording medium and fixing the transferred
image on the recording medium, in which for the toner, the toner of the
present invention is used.

[0070]In the image forming method of the present invention, the surface of
the latent electrostatic image bearing member is uniformly charged in the
charging step. The surface of the latent electrostatic image bearing
member is exposed to form a latent electrostatic image in the exposing
step. The latent electrostatic image formed on the latent electrostatic
image bearing member is developed using a toner to form a visible image
in the developing step. The visible image is transferred onto a recording
medium in the transferring step. The transferred image is fixed on the
recording medium in the fixing step. In the image formation process,
since the toner of the present invention is used, it is possible to form
extremely high-quality images over a long period of time without
substantially causing a change in color tone and abnormal images such as
reduction in image density and background smear.

[0071]The process cartridge of the present invention has at least a latent
electrostatic image bearing member and a developing unit configured to
develop a latent electrostatic image formed on the latent electrostatic
image bearing member using a toner to form a visible image. Because the
process cartridge is detachably mounted to a main body of an image
forming apparatus and is excellent in convenience, and the toner of the
present invention is used, it is possible to form extremely high-quality
images over a long period of time without substantially causing a change
in color tone and abnormal images such as reduction in image density and
background smear.

[0072]The present invention can solve the aforementioned conventional
problems and provide a toner which is excellent in all the properties of
low-temperature fixing property, offset resistance, storage stability,
charge rising property, charge stability with time and pulverizability
and allows for forming high-quality images over a long period of time.
The present invention can also provide an image forming apparatus, an
image forming method and a process cartridge each of which uses the toner
and allows for forming extremely high-quality images over a long period
of time without substantially causing a change in color tone and abnormal
images such as reduction in image density and background smear.

[0073]Because the toner of the present invention is excellent in all the
properties of low-temperature fixing property, offset resistance, storage
stability, charge rising property, charge stability with time and
pulverizability, it is suitably used in electrophotographic image forming
apparatuses, image forming methods, developers, toner containers and
process cartridges.

[0074]Because the image forming apparatus, the image forming method and
the process cartridge of the present invention respectively use the toner
of the present invention and respectively allow for forming extremely
high-quality images over a long period of time without substantially
causing a change in color tone and abnormal images such as reduction in
image density and background smear, they can be widely used for, for
example, laser printers, direct digital photoengraving machines,
full-color copiers based on a direct or indirect electrophotographic
multi-color image developing method, full-color laser printers and
full-color regular paper facsimiles and the like.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0075]FIG. 1 is a cross-sectional view schematically showing one example
of a charging roller used in an image forming apparatus of the present
invention.

[0076]FIG. 2 is a schematic view showing one example of using a contact
type charging roller used in an image forming apparatus of the present
invention.

[0077]FIG. 3 is a schematic view showing one example of using a
non-contact type corona charger in an image forming apparatus of the
present invention.

[0078]FIG. 4 is a schematic view showing one example of a non-contact
charging roller in an image forming apparatus of the present invention.

[0079]FIG. 5 is a schematic view showing one example of a one-component
developing unit in an image forming apparatus of the present invention.

[0080]FIG. 6 is a schematic view showing one example of a two-component
developing unit in an image forming apparatus of the present invention.

[0081]FIG. 7 is a schematic view showing one example of a direct transfer
tandem-type image forming apparatus of the present invention.

[0082]FIG. 8 is a schematic view showing one example of an indirect
transfer tandem-type image forming apparatus of the present invention.

[0083]FIG. 9 is a schematic view showing one example of a belt fixing unit
in an image forming apparatus of the present invention.

[0084]FIG. 10 is a schematic view showing one example of a heat roller
fixing unit in an image forming apparatus of the present invention.

[0085]FIG. 11 is a schematic view showing one example of an
electromagnetic induction heating type fixing unit in an image forming
apparatus of the present invention.

[0086]FIG. 12 is a schematic view showing another example of an
electromagnetic induction heating type fixing unit in an image forming
apparatus of the present invention.

[0087]FIG. 13 is a schematic view showing one example of a cleaning blade
in an image forming apparatus of the present invention.

[0088]FIG. 14 is a schematic view showing one example of a cleaning-less
type image forming apparatus of the present invention.

[0089]FIG. 15 is a schematic view showing one example of an image forming
apparatus of the present invention.

[0090]FIG. 16 is a schematic view showing another example of an image
forming apparatus of the present invention.

[0091]FIG. 17 is a schematic view showing one example of a tandem-type
image forming apparatus of the present invention.

[0093]FIG. 19 is a schematic view showing one example of a process
cartridge of the present invention.

[0094]FIG. 20 is a schematic view showing the image forming apparatus
(evaluation system A) used in the Examples of the present invention.

[0095]FIG. 21 is a schematic view showing the image forming apparatus
(evaluation system B) used in the Examples of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(Toner)

[0096]The toner of the present invention contains at least a binder resin,
a colorant and a charge controlling agent and contains a releasing agent,
external additive and other components in accordance with necessity.

<Binder Resin>

[0097]The binder resin contains a polyester resin (A) having a softening
point Tm (A) of 120° C. to 160° C. and a polyester resin
(B) having a softening point Tm (B) of 80° C. to less than
120° C., and these polyester resins (A) and (B) can be obtained by
condensation polymerizing an alcohol component with a carboxylic acid
component.

[0098]The softening point Tm (A) of the polyester resin (A) is 120°
C. to 160° C., preferably 130° C. to 155° C., and
more preferably 135° C. to 155° C.

[0099]The softening point Tm (B) of the polyester resin (B) is 80°
C. to less than 120° C., preferably 85° C. to 115°
C., and more preferably 90° C. to 110° C.

[0101]The mass ratio [(A)/(B)] of the polyester resin (A) to the polyester
resin (B) is preferably 1/9 to 9/1, more preferably 2/8 to 8/2, and still
more preferably 3/7 to 7/3.

[0102]The polyester resin (A) having a high-softening point provided with
the above-noted physical properties contributes to enhancement of offset
resistance, and the polyester resin (B) having a low-softening point
provided with the above-noted physical properties contributes to
enhancement of low-temperature fixing property. Thus, the use of a
combination of the polyester resin (A) with the polyester resin (B) is
effective to obtain both low-temperature fixing property and offset
resistance.

[0103]In the present invention, at least any one of the polyester resin
(A) and the polyester resin (B) contains 1,2-propane diol at a content of
65 mol % or more in a divalent alcohol component and can be obtained by
condensation polymerizing an alcohol component substantially composed of
only an aliphatic alcohol with a carboxylic acid component.

--Alcohol Component--

[0104]The 1,2-propane diol which is a branched-chain alcohol having 3
carbon atoms used in the alcohol component is more effective in enhancing
the low-temperature fixing property of the toner while maintaining its
offset resistance than use of an alcohol having 2 or less carbon atoms
and is more effective in preventing storage stability degradation
associated with a reduction in glass transition temperature than use of a
branched-chain alcohol having 4 or more carbon atoms. The 1,2-propane
diol can exert effects that it allows for fixing an image at an extremely
low temperature and improving storage stability of the toner. Further, a
polyester rein containing 1,2-propane diol as an alcohol component has
excellent dispersibility with the aromatic oxycarboxylic acid metal
compound having a trivalent or more central metal, and is excellent in
charge rising property. A study of the present inventors showed that
particularly when 1,2-propane diol is contained at a content of 65 mol %
or more in a divalent alcohol component, the dispersibility of the
1,2-propane diol is extremely excellent and the charge amount
distribution of toner is extremely sharp, the mechanical strength of the
toner is improved, and it is also possible to prevent a reduction in
charging property with time that could be caused by being stirred and
shared in a developing device. The reason can be presumed as follows:
because the aromatic oxycarboxylic acid metal compound is finely
dispersed in the polyester resin, a filler-effect is exerted and
consequently, the mechanical strength of the toner is improved.

[0105]The alcohol component may contain alcohols other than 1,2-propane
diol to such an extent not to impair the purpose and effects of the
present invention, however, the content of 1,2-propane diol in a divalent
alcohol component is 65 mol % or more, preferably 70 mol % or more, more
preferably 80 mol % or more, and still more preferably 90 mol % or more.
Examples of the divalent alcohol components other than 1,2-propane diol
include 1,3-propane diol, ethylene glycols each having a different carbon
atoms, hydrogenated bisphenol A or aliphatic dialcohols such as alkylene
(having 2 to 4 carbon atoms) oxide adducts (the average addition number
of moles: 1 to 16).

[0107]It is preferable that the alcohol component of the polyester resin
(A) contain 1,3-propane diol from the perspective of offset resistance.
The molar ratio of 1,2-propane diol to 1,3-propane diol (1,2-propane
diol/1,3-propane diol) in the polyester resin (A) is preferably 99/1 to
65/35, more preferably 95/5 to 70/30, still more preferably 90/10 to
75/25, and particularly preferably 85/15 to 77/23.

[0108]The alcohol component of any one of the polyester resins (A) and (B)
may contain aromatic alcohol such as bisphenol A alkylene oxide adducts
of polyoxypropylene (2,2)-2,2-bis(4-hydroxyphenyl) propane,
polyoxyethylene (2,2)-2,2-bis(4-hydroxyphenyl) propane or the like,
however, the alcohol component of at least any one of the polyester
resins (A) and (B) is virtually composed of only aliphatic alcohol(s),
and preferably both alcohol components of the polyester resins (A) and
(B) are virtually composed of only aliphatic alcohols.

[0109]Here, in the present invention, the terms "alcohol component
virtually composed of only aliphatic alcohol(s)" means that the content
of aliphatic alcohol(s) is 90 mol % or more in the alcohol component, and
the content of aliphatic alcohol(s) is more preferably 95 mol % or more,
still more preferably 98 mol % or more, and particularly preferably 99
mol % or more in the alcohol component.

--Carboxylic Acid Component--

[0110]The carboxylic acid component is not particularly limited and may be
suitably selected in accordance with the intended use, however, it is
preferred that the carboxylic acid component contains an aliphatic
dicarboxylic acid compound having 2 to 4 carbon atoms. Examples of the
aliphatic dicarboxylic acid compound having 2 to 4 carbon atoms include
adipic acids, maleic acids, malic acids, succinic acids, fumaric acids,
citraconic acids, itaconic acids or anhydrides of these acids. Of these,
from the perspective of effectiveness of enhancing low-temperature fixing
property, at least one aliphatic dicarboxylic acid compound selected from
succinic acids, fumaric acids, citraconic acids and itaconic acids is
preferable, and an aliphatic dicarboxylic acid compound of itaconic acid
is particularly preferable.

[0111]The content of the aliphatic dicarboxylic acid having 2 to 4 carbon
atoms is preferably 0.5 mol % to 20 mol % and more preferably 1 mol % to
10 mol % in the carboxylic acid component from the perspective of
enhancing low-temperature fixing property and preventing a reduction in
glass transition temperature. Because a polyester resin that can be
obtained by condensation polymerizing such an aliphatic carboxylic acid
compound having no aromatic ring with 1,2-propane diol has excellent
solubility with releasing agents, the use of the polyester resin together
with a releasing agent can further improve the toner filming resistance.

[0112]Further, it is preferable that the carboxylic component contain
rosin. By using a rosin having a polycyclic aromatic ring,
water-absorbing property of conventional aliphatic alcohol polyesters can
be lowered, and an effect of preventing reductions in charge amount of
toner under high-temperature and high-humidity conditions is further
improved.

[0113]The rosin is a natural resin obtainable from pines, and the main
component is a resin acid such as abietic acid, neoabietic acid,
palustric acid, pimaric acid, isopimaric acid, sandaracopimaric acid and
dehydroabietic acid or a mixture thereof.

[0114]The rosins are broadly classified into tall rosins obtainable from
tall oils that can be obtained as by-products in a pulp manufacturing
process, gum rosins obtainable from crude pine tar and wood rosins
obtainable from pine strains. The rosin used in the present invention is
preferably tall rosin from the perspective of low-temperature fixing
property.

[0115]The rosin may be a modified rosin such as disproportionated rosin
and hydrogenated rosin, however, in the present invention, it is
preferable to use an unmodified rosin, a so-called crude rosin, from the
perspective of low-temperature fixing property and storage stability.

[0116]The rosin is preferably purified from the perspective of enhancing
storage stability and deodorization.

[0117]The purified rosin is a rosin whose impurities are removed in a
purification process. Examples of major impurities 2-methylpropane,
acetaldehyde, 3-methyl-2-butanone, 2-methyl propanoic acid, butanoic
acid, pentanoic acid, n-hexanal, octane, hexanoic acid, benzaldehyde,
2-pentylfuran, 2,6-dimethyl cyclohexanone, 1,
methyl-2-(1-methylethyl)benzene, 3,5-dimethyl 2-cyclohexane and
4-(1-methylethyl)benzaldehyde. In the present invention, of these
impurities, peak intensities in three types of impurities of 2-methyl
propane, pentanoic acid and benzaldehyde detected as volatile components
in the Head-Space GC-MS analysis can be used as indicators of purified
rosins. The reason why the volatile component of impurities is used as an
indicator instead of using those absolute amounts is that a purified
rosin is used to deodorize conventional polyester resins using rosin and
the deodorization therefrom is addressed as one of the problems to solve
in the present invention.

[0118]In the present invention, a purified rosin means a rosin that has a
peak intensity of hexanoic acid of 0.8×107 or less, a peak
intensity of pentanoic acid of 0.4×107 or less and a peak
intensity of benzaldehyde of 0.4×107 or less under the
following measurement conditions for the Head-Space GC-MS analysis. From
the viewpoint of storage stability and deodorization of the polyester
resin, a peak intensity of hexanoic acid is preferably 0.6×107
or less and more preferably 0.5×107 or less. The peak
intensity of pentanoic acid is preferably 0.3×107 or less and
more preferably 0.2×107 or less. The peak intensity of
benzaldehyde is preferably 0.3×107 or less and more preferably
0.2×107 or less.

[0119]From the viewpoint of storage stability and deodorization of the
polyester resin, besides the content of the above-noted three impurities,
it is preferable that the content of n-hexanal and 2-pentylfuran be
reduced. The peak intensity of n-hexanal is preferably 1.7×107
or less, more preferably 1.6×107 or less, and still more
preferably 1.5×107 or less. The peak intensity of
2-pentylfuran is preferably 1.0×107 or less, more preferably
0.9×107 or less, and still more preferably 0.8×107
or less.

[0120]A purification method of the rosin is not particularly limited and
conventional methods can be utilized. Examples of thereof include
distillation, re-crystallization, and extraction. It is preferable to
purify a crude rosin by distillation. For the distillation method, for
example, the methods described in Japanese Patent Application Laid-Open
(JP-A) No. 7-286139 can be utilized, and reduced-pressure distillation,
molecular distillation and steam distillation are exemplified. It is
preferable to purify a crude rosin by distillation under reduced
pressure. For example, distillation is generally carried out under a
pressure of 6.67 kPa or less and a still temperature of 200° C. to
300° C., and simple distillation is commonly used, and other
methods such as thin-film distillation and rectification distillation are
used. Under a typical distillation condition, 2% by mass to 10% by mass
of high-molecular weight material to the content of the placed rosin is
removed as a pitch and 2% by mass to 10% by mass of an initial distillate
is removed at the same time.

[0121]The softening point of the purified rosin is preferably 50°
C. to 100° C., more preferably 60° C. to 90° C., and
still more preferably 65° C. to 85° C. Impurities contained
in the rosin can be removed by subjecting a rosin to a purification
treatment. The softening point of the purified rosin in the present
invention means a softening point that is measured when the purified
rosin is once fused by the following method and thereafter naturally
cooled under the condition of a temperature of 25° C. and a
relative humidity of 50% for 1 hour.

[0122]The acidic value of the purified rosin is preferably 100 mgKOH/g to
200 mgKOH/g, more preferably 130 mgKOH/g to 180 mgKOH/g, and still more
preferably 150 mgKOH/g to 170 mgKOH/g. The content of the purified rosin
in the carboxylic acid component is preferably 2 mol % to 50 mol %, more
preferably 5 mol % to 40 mol %, and still more preferably 10 mol % to 30
mol %.

[0123]The carboxylic acid component may contain carboxylic acid compounds
other than the aliphatic carboxylic acid compound and the rosin to such
an extent not to impair the effects of the present invention. From the
perspective of ensuring the glass transition temperature of the
carboxylic acid component, it is preferable that aromatic dicarboxylic
acids such as phthalic acid, isophthalic acid and terephthalic acid be
contained in the carboxylic acid component. The content of the aromatic
dicarboxylic acid in the carboxylic acid component is preferably 40 mol %
to 95 mol %, more preferably 50 mol % to 90 mol %, and still more
preferably 60 mol % to 80 mol %.

[0124]It is preferred that the polyester resins are respectively a
crosslinked polyester resin, and a trivalent or more raw material monomer
is contained as a crosslinking agent in at least any one of the alcohol
component and the carboxylic acid component. The content of the trivalent
or more raw material monomer in the total amount of the alcohol component
and the carboxylic acid component is preferably 0 mol % to 40 mol % and
more preferably 5 mol % to 30 mol %.

[0125]For trivalent or more of polyvalent carboxylic acid compounds used
for the trivalent or more raw material monomers, for example, trimellitic
acids or derivatives thereof are preferably exemplified. Examples of
trivalent or more polyvalent alcohols include glycerine, pentaerythritol,
trimethylolpropane, sorbitol or alkylene (having 2 to 4 carbon atoms)
oxide adducts (the average addition number of moles: 1 to 16). Of these,
glycerine is particularly preferable because it functions as a
crosslinking agent but is also effective in enhancing low-temperature
fixing property. From these viewpoints, it is preferable that the alcohol
component of at least any one of the polyester resins (A) and (B) contain
glycerine. The content of the glycerine in the alcohol component is
preferably 5 mol % to 40 mol % and more preferably 10 mol % to 35 mol %.

--Esterified Catalyst--

[0126]Condensation polymerization of the alcohol component with the
carboxylic acid component is preferably carried out in the presence of an
esterification catalyst. Examples of the esterification catalyst include
Lewis acids such as p-toluene sulfonate, titanium compounds, and tin (II)
compounds having no Sn--C bond, and each of these esterification
catalysts may be used alone or in combination with two or more. Of these,
a titanium compound and a tin (II) compound having no Sn--C bond are
particularly preferable.

[0127]For the titanium compound, a titanium compound having a Ti--O bond
is preferable, and a compound having an alkoxy group, an alkenyloxy group
or an acyloxy group each having the total number of carbon atoms of 1 to
28 is more preferable.

[0130]The presence amount of the titanium compound to 100 parts by mass of
the total amount of the alcohol component and the carboxylic acid
component is preferably 0.01 parts by mass to 1.0 part by mass and more
preferably 0.1 parts by mass to 0.7 parts by mass.

[0131]For the tin (II) compound having no Sn--C bond include, a tin (II)
compound having an Sn-0 bond and a tin (II) compound having an Sn--X bond
("X" represents a halogen atom) are preferable, and a tin (II) compound
having an Sn-0 bond is more preferable.

[0133]Examples of the compound having an Sn--X bond ("X" represents a
halogen atom) include halogenated tins (II) such as tin (II) chlorides
and tin (II) bromides. Of these, from the viewpoints of charge rising
effect and catalytic ability, fatty acid tin (II) represented by
(R1COO)2Sn (R1 represents an alkyl group or an alkenyl
group having 5 to 19 carbon atoms), dialkoxy tin (II) represented by
(R2O)2Sn (R2 represents an alkyl group or an alkenyl group
having 6 to 20 carbon atoms), and tin (II) oxide represented by SnO are
preferable. Fatty acid tin (II) represented by (R1COO)2Sn and
tin (II) oxide are more preferable. Tin (II) octanoate, tin (II)
distearate and tin (II) oxide are more preferable.

[0134]The presence amount of the tin (II) compound having no Sn--C bond to
100 parts by mass of the total amount of the alcohol component and the
carboxylic acid component is preferably 0.01 parts by mass to 1.0 part by
mass and more preferably 0.1 parts by mass to 0.7 parts by mass.

[0135]When the titanium compound is used together with the tin (II)
compound having no Sn--C bond, the total presence amount of the titanium
compound and the tin (II) compound is preferably 0.01 parts by mass to
1.0 part by mass and more preferably 0.1 parts by mass to 0.7 parts by
mass to 100 parts by mass of the total amount of the alcohol component
and the carboxylic acid component.

[0136]The condensation polymerization of the alcohol component with the
carboxylic acid component can be carried out, for example, in the
presence of the esterification catalyst, in an inert gas atmosphere and
at a temperature of 180° C. to 250° C. The softening point
of the polyester resin can be controlled by the reaction time.

[0137]The grass transition temperature of the polyester resins (A) and (B)
is preferably 45° C. to 75° C., more preferably 50°
C. to 70° C. and still more preferably 50° C. to 65°
C. from the perspective of fixing ability, storage stability and
durability. The acidic value of the polyester resins (A) and (B) is
preferably 1 mgKOH/g to 80 mgKOH/g and more preferably 10 mgKOH/g to 50
mgKOH/g.

[0138]In the present invention, it is preferable that the polyester resins
(A) and (B) be respectively an amorphous polyester, which differs from
crystalline resins. In the present invention, the term "amorphous
polyester" means a polyester of which the softening point temperature is
30° C. or higher or 30° C. or lower than the glass
transition temperature.

[0139]The polyester resins (A) and (B) may by a modified polyester resin.
The modified polyester resin means a polyester resin that is grafted or
blocked with phenol, urethane or the like.

[0140]In the binder resin, conventionally known binder resins, for
example, vinyl resin such as styrene-acrylic resin and other resins such
as epoxy resin, polycarbonate and polyurethane may be used in
combination, however, the total content of the polyester resin (A) and
the polyester resin (B) in the binder resin is preferably 70% by mass or
more, more preferably 80% by mass or more, still more preferably 90% by
mass or more, and particularly preferably 100% by mass.

[0142]For the aromatic oxycarboxylic acid metal compound having a
trivalent or more central metal, for example, a compound represented by
the following General Formula (1) is preferable.

[0143]In the General Formula (1), R1 represents any one of a carbon
atom, a methine group and a methylene group, the methine group and the
methylene group may respectively contain a hetero atom selected from N, S
and P; "Y" represents a ring structure linked by saturated bond(s) or
unsaturated bond(s); R2 and R3 respectively represent a
hydrogen atom, a halogen atom, a hydroxyl group, a nitro group, a nitroso
group, a sulfonyl group, a cyano group, an alkyl group, alkenyl group, an
alkoxy group, an aryl group, an aryloxy group, an aralkyl group, an
aralkyloxy group, an amino group, a carboxyl group and a carbonyl group,
and when "o" and "p" are respectively an integer of 1 or more, R2
and R3 may be the same to each other or different from each other,
and R2 and R3 may be further substituted by a substituent
group; R4 represents any one of a hydrogen atom and an alkyl group;
"1" is zero or an integer of 3 to 12; "m" is an integer of 1 to 20; "n"
is zero or an integer of 1 to 20; "o" is zero or an integer of 1 to 4;
"p" is zero or an integer of 1 to 4; "q" is zero or an integer of 1 to 3;
"r" is an integer of 1 to 20; "s" is zero or an integer of 1 to 20; and
"M" is a trivalent or more central metal.

[0150]Examples of the substituent group that is represented by the R2
or R3 and may be further substituted by a substituent group include
alkyl group such as halogen atom, nitro group, cyano group, methyl group
and ethyl group, alkoxy group such as methoxy group and ethoxy group,
aryl oxy group such as phenoxy group, aryl group such as phenyl group and
nephthyl group, and aralkyl groups.

[0151]Examples of the ring structure represented by Y include aliphatic
rings, aromatic rings and heterocyclic rings.

[0152]When R4 is a hydrogen atom, the aromatic oxycarboxylic acid
metal compound sometimes contains a structure represented by the
following General Formula (3), and such an aromatic oxycarboxylic acid
metal compound can also be used without causing problems.

[0153]In the General Formula (3), R1, R2, R3, Y, M, "l",
"m", "n", "o", "p", "q" and "r" respectively have the same meaning as
those described in the General Formula (1).

[0154]The central metal "M" is not particularly limited and any trivalent
or more metal can be used, however, preferred examples thereof are Fe,
Ni, Al, Ti and Zr. Of these metals, Fe and Zr are particularly preferable
because of the excellent charge rising property. Further, Fe is
preferably used in terms of safety, and Zr is preferably used in terms
that the compound is white and suitable for color toner. When the
aromatic oxycarboxylic acid metal compound has a trivalent or more
central metal, it is extremely excellently dispersible in a polyester
resin containing 1,2-propane diol as an alcohol component and is also
excellent in charge rising property. In contrast, when the aromatic
oxycarboxylic acid metal compound has a divalent central metal, it cannot
be excellently dispersed in such a polyester resin, although it is
excellent in charge resizing property. Therefore, it is impossible to
obtain an effect of preventing a reduction in charge amount that could be
caused by time degradation of toner. Thus, the aromatic oxycarboxylic
acid metal compound having a trivalent or more central metal is
preferably a compound represented by the General Formula (1).

[0155]The aromatic oxycarboxylic acid site in the aromatic oxycarboxylic
acid metal compound having a trivalent or more central metal can be
represented by the following General Formula (2).

[0156]In the General Formula (2), it is preferable that R5, R6,
R7 and R8 respectively represent a hydrogen atom, a straight
chain alkyl group having 1 to 18 carbon atoms, a branched alkyl group
having 1 to 18 carbon atoms or an aryl group, and R5, R6,
R7 and R8 may be the same to each other or different from each
other, further, R5 and R6, R6 and R7, R7 and
R8 may be respectively linked to each other to form an aromatic ring
that may have a substituent group or an aliphatic ring that may have a
substituent group.

[0157]Examples of the alkyl group and aryl group in the General Formula
(2) are those described in the General Formula (1).

[0158]Hereinafter, specific examples of the aromatic oxycarboxylic acid
site represented by the General Formula (2) will be described, however,
the examples thereof are not limited to the disclosed examples.

[0160]Hereinafter, specific examples of the aromatic oxycarboxylic acid
metal compound represented by the General Formula (1) will be described,
however, the examples thereof are not limited to the disclosed examples.
Each of these compounds may be used alone or in combination with two or
more. In the following structural formulas, "t-Bu" represents a tertiary
butyl group.

[0161]The content of the aromatic oxycarboxylic acid metal compound having
a trivalent or more central metal in the toner cannot be unequivocally
described because it is determined by the toner production method used
including the composition of resins and dispersion method, however, it is
preferably 0.1 parts by mass to 10 parts by mass, more preferably 0.5
parts by mass to 5 parts by mass, and still more preferably 0.5 parts by
mass to 2 parts by mass to 100 parts by mass of the binder resin. When
the content of the aromatic oxycarboxylic acid metal compound having a
trivalent or more central metal is less than 0.1 parts by mass, an effect
of obtaining excellent charge rising property and an effect of preventing
a reduction in charge stability with time are hardly obtained, and when
the content is more than 10 parts by mass, it may result in an
excessively charged amount of toner and/or impaired low-temperature
fixing property of the toner.

[0162]In the toner of the present invention, conventionally known charge
controlling agents may be used in combination in accordance with
necessity. The charge controlling agents are not particularly limited and
may be suitably selected in accordance with the intended use, and
examples thereof include triphenylmethane dyes, molybdenum acid chelate
pigments, Rhodamine dyes, alkoxy amines, quaternary ammonium salts
(including fluorine-modified quaternary ammonium salts), alkyl amides,
phosphorous monomers or compounds thereof, tungsten monomers or compounds
thereof, fluorine activators, metal salts of salicylic acid and metal
salts of salicylic acid derivatives. Each of these charge controlling
agents may be used alone or in combination with two or more.

[0163]The charge controlling agents may be fused and kneaded with the
masterbatch and thereafter dissolved or dispersed in the masterbatch, or
may be directly dissolved or dispersed together with the respective toner
components in the organic solvent or may be fixed on the toner surface
after toner particles are produced.

[0165]The color of the colorant is not particularly limited, may be
suitably selected in accordance with the intended use, and examples
thereof include colorants for black and colorants for color. Each of
these colorants may be used alone or in combination with two or more.

[0170]The content of the colorant(s) in the toner is not particularly
limited and may be suitably selected in accordance with the intended use,
however, it is preferably 1% by mass to 15% by mass and more preferably
3% by mass to 10% by mass. When the content of the colorant(s) is less
than 1% by mass, a reduction in coloring power of the toner is observed,
and when more than 15% by mass, the pigment is not sufficiently dispersed
in the toner and this may cause a reduction in coloring power of the
toner and/or a reduction in electric properties of the toner.

[0171]The colorant(s) may be used as a masterbatch that is complexed with
resin(s). The resin is not particularly limited and may be suitably
selected from among conventional resins in accordance with the intended
use. Examples of the resin include styrenes or polymers of the
substituents thereof, styrene copolymers, polymethyl methacrylate resins,
polybutyl methacrylate resins, polyvinyl chloride resins, polyvinyl
acetate resins, polyethylene resins, polypropylene resins, polyester
resins, epoxy resins, epoxy polyol resins, polyurethane resins, polyamide
resins, polyvinyl butyral resins, polyacrylic acid resins, rosins,
modified rosins, terpene resins, aliphatic hydrocarbon resins,
cycloaliphatic hydrocarbon resins, aromatic petroleum resins, chlorinated
paraffins and paraffins. Each of these resins may be used alone or in
combination with two or more.

[0173]The masterbatch can be produced by mixing or kneading the resin(s)
for masterbatch with the colorant under a high-shearing force. At the
time of the mixing or kneading, to promote mutual interaction between the
colorant and the resin(s), it is preferable to add an organic solvent.
Further, a wet cake of a colorant can also be directly used in a
so-called flashing process, which is preferably used in terms that it
requires no need to dry the colorant wet cake. In the flashing process, a
colorant-water-paste containing water is mixed and kneaded with resins
and an organic solvent to transfer the colorants to the resins and then
to remove the moisture and the organic solvent components. For the mixing
and kneading, a high shearing dispersion unit such as a triple roll mill
is preferably used.

--Releasing Agent--

[0174]The releasing agent is not particularly limited and may be suitably
selected from among conventional releasing agents in accordance with the
intended use. Examples of the releasing agent include carbonyl
group-containing waxes, polyolefine waxes and waxes such as long-chain
hydrocarbons. Each of these may be used alone or in combination with two
or more. Of these, carbonyl group-containing waxes are preferable.

[0176]Examples of the polyolefine waxes include polyethylene waxes and
polypropylene waxes.

[0177]Examples of the long-chain hydrocarbons include paraffin waxes and
sazol waxes.

[0178]The melting point of the releasing agent is not particularly limited
and may be suitably adjusted in accordance with the intended use,
however, it is preferably 40° C. to 160°, more preferably
50° C. 120°, and still more preferably 60° C. to
90° C. When the melting point of the releasing agent is lower than
40° C., it may adversely affect the heat resistance/storage
stability of the toner, and when higher than 160° C., cold-offset
may easily occur at the time of fixing an image at a low-temperature.

[0179]The melting point of the releasing agent can be determined, for
example, by the following method. The temperature of a sample is
increased to 200° C. using a differential scanning calorimetry
(DSC210, manufactured by Seiko Electronics Industries Co., Ltd.), the
sample is cooled down from that temperature to 0° C. at a
temperature decreasing rate of 10° C./min and then increased at a
temperature increasing rate of 10° C./min, and the maximum peak of
heat-melting temperature can be determined as the melting point of the
sample.

[0180]The melt viscosity of the releasing agent as a value measured at a
temperature 20° C. higher than the melting point of the wax, is
preferably 5 cps to 1,000 cps and more preferably 10 cps to 100 cps. When
the melt viscosity of the releasing agent is lower than 5 cps, the
releasing property of the toner may degrade, and when higher than 1,000
cps, an effect of promoting hot-offset resistance and low-fixing property
may not be obtained.

[0181]The content of the releasing agent in the toner is not particularly
limited and may be suitably selected in accordance with the intended use,
however, it is preferably 0% by mass to 40% by mass and more preferably
3% by mass to 30% by mass.

[0182]When the content of the releasing agent is more than 40% by mass,
the flowability of the toner may degrade.

[0185]The hydrophobized silica fine particle, hydrophobized titania fine
particle or hydrophobized alumina fine particle can be obtained by
subjecting a hydrophilic fine particles to a hydrophobizing treatment
with the use of a silane coupling agent as hydrophobizing agent such as
methyl trimethoxy silane, methyl triethoxy silane and octyl trimethoxy
silane.

[0187]Further, an inorganic fine particle treated with silicone oil of
which an inorganic fine particle is hydrophobized by application of heat
if necessary is preferably used as the hydrophobizing treatment agent.

[0190]The average primary particle diameter of the inorganic fine particle
is preferably 1 nm to 100 nm and more preferably 3 nm to 70 nm. When the
average particle diameter is less than 1 nm, the inorganic fine particle
is embedded in the toner and the function is sometimes rarely exerted
efficiently, and when more than 100 nm, the surface of a latent
electrostatic image bearing member may be damaged nonuniformly. For the
external additives, it is possible to use an inorganic fine particle with
a hydrophobized inorganic fine particle, however, the average primary
particle diameter of the hydrophobized inorganic fine particle is
preferably 1 nm to 100 nm and more preferably 5 nm to 70 nm. It is
preferable that the external additives contain at least two types of
hydrophobized inorganic fine particles each having an average primary
particle diameter of 20 nm or less and at least one inorganic fine
particle having an average primary particle diameter of 30 nm or more.
The specific surface area of the inorganic fine particle measured by the
BET method is preferably 20 m2/g to 500 m2/g.

[0191]The additive amount of the external additives to the amount of the
toner is preferably 0.1% by mass to 5% by mass and more preferably 0.3%
by mass to 3% by mass.

[0192]A resin fine particle can also be added as the external additive.
Examples of the resin fine particle include polystyrene that can be
obtained, for example, by soap-free emulsification polymerization,
suspension polymerization or dispersion polymerization; copolymers of
methacrylic acid esters and acrylic acid esters; condensation-polymerized
fine particles composed of silicone, benzoguanamine, nylon or the like;
and polymer particles composed of thermosetting resin. By using such a
resin fine particle in combination, the charge property of the toner can
be enhanced, the amount of reversely charged toner can be reduced and the
occurrence of background smear can be reduced. The additive amount of the
resin fine particle to the amount of the toner is preferably 0.01% by
mass to 5% by mass and more preferably 0.1% by mass to 2% by mass.

--Other Components--

[0193]The other components are not particularly limited and may be
suitably selected in accordance with the intended use, and examples
thereof include flowability improving agents, cleaning ability improving
agents, magnetic materials and metal soaps.

[0194]The flowability improving agent is used in surface treatment of the
toner to increase the hydrophobic property of the toner and enables to
prevent degradation of the flowability and charge property of the toner
even under a high-humidity condition. Examples of the flowability
improving agent include silane coupling agents, silylation agents, silane
coupling agents having an alkyl fluoride group, organic titanate coupling
agents, aluminum coupling agents, silicone oils and modified silicone
oils.

[0195]The cleaning improving agent is added to the toner to remove a
residual developer remaining on a latent electrostatic image bearing
member and an intermediate transfer member after transferring the toner.
Examples of the cleaning improving agent include fatty acid metal salts
of zinc stearates, calcium stearates, stearic acids and the like; and
polymer fine particles produced by soap-free emulsion polymerization such
as polymethyl methacrylate fine particles and polystyrene fine particles.
For the polymer fine particle, it is preferable to use a polymer fine
particle having a relatively narrow particle size distribution and a
volume average particle diameter of 0.01 μm to 1 μm.

[0196]The magnetic material is not particularly limited and may be
suitably selected from among conventional magnetic materials in
accordance the intended use. Examples thereof include iron powders,
magnetites and ferrites. Of these, white ones are preferable in terms of
color tone.

--Toner Production Method--

[0197]The toner production method is not particularly limited and may be
suitably selected from conventionally known toner production methods in
accordance with the intended use. For example, kneading pulverization
method, polymerization method, dissolution suspension method and spray
granulation method are exemplified.

[0198]Of these, kneading-pulverizing method is particularly preferable
from the perspective of dispersibility of the aromatic oxycarboxylic acid
metal compound and colorants and the productivity.

Kneading Pulverization Method--

[0199]In the kneading pulverization method, for example, a toner material
containing at least a binder resin and a colorant is melted and kneaded,
and the obtained kneaded product is pulverized and classified to thereby
produce a base particle of the toner.

[0200]In the melting and kneading of the toner material, the toner
material is mixed and the mixture is placed in a melting kneader to melt
and knead the mixture. For the melting kneader, for example, a uniaxial
or biaxial continuous kneader or a batch type kneader such as a roller
mill can be used. For example, KTK type biaxial extruder manufactured by
KOBE STEEL., LTD.; TEM type biaxial extruder manufactured by TOSHIBA
MACHINE CO., LTD.; biaxial extruder manufactured by KCK Co., Ltd.; PCM
type biaxial extruder manufactured by IKEGAI, LTD. and continuous type
uniaxial extruder such as Co-kneader manufactured by BUSS are preferably
used. It is preferable that the melting and kneading be carried out under
such appropriate conditions not to cut molecular chains of the binder
resin.

[0201]Specifically, the melting kneading temperature is set in reference
to the softening point of the binder resin. When the melting kneading
temperature is excessively higher than the softening point, the molecular
chains of the binder resin are severely cut off, and when excessively
lower than the softening point, the dispersion of the toner material may
not proceed.

[0202]In the pulverization, the kneaded product obtained in the kneading
is pulverized. In the pulverization, it is preferred that first the
kneaded product be coarsely crushed and then finely pulverized. It is
also preferred that the toner material mixture be pulverized by making
particles collide with a collision plate or making particles collide with
each other in a jet stream or pulverizing the toner mixture particles in
a narrow gap between a mechanically rotatable rotor and a stator.

[0203]In the classification of particles, the pulverized material obtained
in the pulverization is classified to prepare particles having
predetermined particle diameters. The classification can be carried out
by removing fine particles using, for example, a cyclone, a decanter, a
centrifugal separator or the like.

[0204]After completion of the pulverization and classification, the
pulverized material is classified in a stream by applying a centrifugal
force thereto, thereby producing a toner base particle having
predetermined particle diameters.

[0205]Next, external additives are externally added to the toner base
particle. By mixing and stirring the toner base particle and the external
additives using a mixer, the toner base particle surface is coated with
the external additives with the external additive being dissolved and
pulverized. Here, it is important to make the external additives such as
an inorganic fine particle, a resin fine particle and the like uniformly
and strongly adhere on the toner base particle in terms of the durability
of the toner.

--Polymerization Method--

[0206]In the toner production method based on the polymerization method,
for example, a toner can be produced by dissolving or dispersing a toner
material containing at least a modified polyester resin that can form a
urea bonding or urethane bonding and a colorant in an organic solvent,
dispersing the dissolved or dispersed material in an aqueous medium,
applying a polymerization addition reaction thereto, and removing the
solvent of the dispersion liquid and washing the dispersion.

[0207]For the modified polyester resin that can form a urea bonding or
urethane bonding, a polyester prepolymer having an isocyanate group in
which a carboxyl group, a hydroxyl group or the like is reacted with a
polyvalent isocyanate compound (PIC) is exemplified. Then, a modified
polyester resin that can be obtained by crosslinking and/or elongating
the molecular chains in a reaction between the polyester prepolymer and
amines or the like can improve the hot offset property of the toner while
maintaining the low-temperature fixing property.

[0208]Examples of the polyvalent isocyanate compound (PIC) include fatty
acid polyvalent isocyanate (such as tetramethylene diisocyanate,
hexamethylene diisocyanate, and 2,6-diisocyanate methyl caproate);
cycloaliphatic polyisocyanate (such as isophorone diisocyanate, and
cyclohexyl methane diisocyanate); aromatic diisocyanate (such as tolylene
diisocyanate, and diphenyl methane diisocyanate); aromatic aliphatic
diisocyanate (α,α,α',α'-tetramethyl xylene
diisocyanate, etc.); isocyanates; and the polyisocyanates blocked with a
phenol derivative, oxime, caprolactam or the like. Each of these may be
used alone or in combination with two or more.

[0209]The mixture ratio of the polyvalent isocyanate compound (PIC), for
example, the equivalent ratio [NCO]/[OH] of isocyanate group [NCO]
content in the polyisocyanate (PIC) to hydroxyl group [OH] content in the
hydroxyl group-containing polyester is preferably 5/1 to 1/1, more
preferably 4/1 to 1.2/1, and still more preferably 2.5/1 to 1.5/1.

[0210]The number of isocyanate groups contained in one molecule in the
polyester prepolymer (A) having an isocyanate group is preferably one,
more preferably 1.5 to 3 on the average, and still more preferably 1.8 to
2.5 on the average.

[0211]Examples of the amines (B) to be reacted to the polyester prepolymer
include divalent amine compounds (B1), trivalent or more polyvalent amine
compounds (B2), amino alcohols (B3), aminomercaptans (B4), amino acids
(B5) and blocked amines of which amino groups of B1 to B5 are blocked
(B6).

[0213]Examples of the trivalent or more polyvalent amine compound (B2)
include diethylene triamine and triethylene tetramine.

[0214]Examples of the amino alcohol (B3) include ethanol amine and
hydroxyethyl aniline.

[0215]Examples of the aminomercaptan (B4) include aminoethyl mercaptan and
aminopropyl mercaptan.

[0216]Examples of the amino acid (B5) include amino propionate and amino
caproate.

[0217]Examples of the blocked amines of which amino groups of B1 to B5 are
blocked (B6) include ketimine compounds obtainable from the amines of B1
to B5 and ketones (such as acetone, methylethylketone, and
methylisobutylketone), and oxazolidine compounds. Of these amines (B), a
mixture of amines of B1 and B1 and a small amount of amine B2 is
particularly preferable.

[0218]The mixture ratio of the amines (B), for example, the equivalent
ratio of [NCO]/[NHx] of isocyanate group [NCO] content in the polyester
prepolymer (A) having an isocyanate group to amino group [NHx] content in
the amines (B) is preferably 1.2 to 2/1, more preferably 1.5/1 to 1/1.5,
and more preferably 1.2/1 to 1/1.2.

[0219]According to a toner production method based on the polymerization
method stated above, it is possible to produce a spherically shaped toner
having small particle diameter at a low cost without having a significant
impact on environment.

[0220]Color of the toner is not particularly limited and may be suitably
selected in accordance with the intended use and may be suitably selected
in accordance with the intended use. For example, at least one selected
from black toners, cyan toners, magenta toners and yellow toners can be
used. Each color of toners can be selected by suitably selecting the
types of the colorants, and the color toner is preferably a color toner.

[0221]The weight average particle diameter of the toner is not
particularly limited and may be suitably adjusted in accordance with the
intended use. To obtain a high-quality image that is excellent in
granulation degree, image sharpness and thin-line reproductivity, the
weight average particle diameter is preferably 3 μm to 10 μm and
more preferably 4 μm to 7 μm. When the weight average particle
diameter is less than 3 μm, the flowability and transferring property
of the toner may degraded, although the image sharpness and thin-line
reproductivity of images are excellent.

[0222]Here, the weight average particle diameter of the toner can be
measured, for example, as follows.

[0228]Dispersion conditions: 10 milligrams of a measurement sample was
added to 5 mL of the dispersion liquid, and the dispersion liquid was
dispersed in a ultrasonic dispersion device for 1 minute, and then 25 mL
of the electrolyte was added to the dispersion liquid, and the dispersion
liquid was further dispersed in the ultrasonic dispersion device for 1
minute.

[0229]Measurement conditions: 100 mL of the electrolyte and the dispersion
liquid were added to a beaker, 30,000 pieces of particles of the sample
were measured at such a concentration that the particle diameter of
30,000 pieces of particles could be measured for 20 seconds, and the
weight average particle diameter of the sample is determined from the
particle size distribution.

(Developer)

[0230]The developer of the present invention contains at least the toner
of the present invention and contains suitably selected other components
such as carrier. The developer may be a one-component developer or a
two-component developer, however, when used in a high-speed printer or
the like which can respond to recent improvements in information
processing high-speed performance, it is preferable to use the
two-component developer in terms of improvement in operating life of the
printer.

[0231]When the one-component developer using the toner is used, there are
little changes in toner particle diameter, causing less occurrence of
toner filming to a developing roller serving as a developer carrier and
less occurrence of toner fusion to a layer thickness controlling member
such as a blade to make a toner layer thin even when toner inflow/outflow
is performed, and it is possible to obtain excellent developing property
and excellent images with stability even when a developing unit is used
for long hours, i.e., even when the developer is stirred for long hours.
Further, when the two-component developer using the toner is used, there
are little changes in toner particle diameter of the toner in the
developer, and it is possible to obtain excellent developing property
with stability even when the developer is stirred for long hours in a
developing unit.

--Carrier--

[0232]The carrier is not particularly limited and may be suitably selected
in accordance with the intended use, however, a carrier having a core and
a resin layer to cover the core is preferable.

[0233]Material used for the core is not particularly limited and may be
suitably selected from conventional core materials. For example, a
manganese-strontium (Mn--Sr) material or a manganese-magnesium (Mn--Mg)
material of 50 emu/g to 90 emu/g is preferably used. In terms of ensuring
image density, iron powder (100 emu/g or more), or a ferromagnetic
material such as magnetite (75 emu/g to 120 emu/g) is preferably used.
Further, in terms that a contact force applied to a latent electrostatic
image bearing member on which a toner is standing can be weakened and it
is advantageous in obtaining high-quality images, a feebly magnetic
material such as copper-zinc (Cu--Zn) material (30 emu/g to 80 emu/g) is
preferably used. Each of these may be used alone or in combination with
two or more.

[0234]For the particle diameter of the core, the average particle diameter
thereof (volume average particle diameter (D50)) is preferably 10
μm to 200 μm and more preferably 40 μm to 100 μm. When the
average particle diameter (volume average particle diameter (D50))
is less than 10 μm, a large amount of fine powder particles is
observed in the carrier particle distribution, the magnetization
intensity per one particle is lowered, and carrier scattering may occur.
When the average particle diameter (volume average particle diameter
(D50)) is more than 200 μm, the specific surface area of the
toner is decreased, toner scattering may occur. In a full-color image
having a large area ratio of solid parts, the reproductivity of
particularly in the solid parts may degrade.

[0235]Material used for the resin layer is not particularly limited and
may be suitably selected from among conventional resins in accordance
with the intended use. Examples of the material of the resin layer
include amino resins, polyvinyl resins, polystyrene resins, halogenated
olefin resins, polyester resins, polycarbonate resins, polyethylene
resins, polyvinyl fluoride resins, polyvinylidene fluoride resins,
polytrifluoroethylene resins, polyhexafluoro-propylene resins, copolymers
of vinylidene fluoride with acrylic monomer, copolymers of vinylidene
fluoride with vinyl fluoride, fluoroterpolymer (triple
(multiple)-fluoride copolymers) such as terpolymer of
tetrafluoroethylene, vinylidene fluoride and non-fluorinated monomer, and
silicone resins. Each of these may be used alone or in combination with
two or more. Of these, silicone resins are particularly preferable.

[0236]The silicone resin is not particularly limited and may be suitably
selected from among commonly known silicone resins in accordance with the
intended use. Examples thereof include straight silicone resins formed
from only organosiloxane bonding; and silicone resins modified with an
alkyd resin, polyester resin, epoxy resin, acrylic resin, urethane resin
or the like.

[0237]For the silicone resin, a commercially available product can be
used. Specific examples of the commercially available products of the
straight silicone resin include KR271, KR255 and KR152 manufactured by
Shin-Etsu Chemical Co., Ltd.; and SR2400, SR2406 and SR2410 manufactured
by DOW CORNING TORAY SILICONE CO., LTD.

[0239]In addition, it is also possible to singularly use a silicone resin,
and also possible to use a silicone resin in combination with
crosslinkable component(s) and/or charge amount controllable component(s)
and the like.

[0240]To the resin layer, a conductive powder etc. may be added in
accordance with necessity. Examples of the conductive powder include
metal powder, carbon black, titanium oxide, tin oxide and zinc oxide. The
average particle diameter of the conductive powder is preferably 1 μm
or less. When the average particle diameter of the conductive powder is
larger than 1 μm, it may be difficult to control electric resistance
of the toner.

[0241]The resin layer can be formed, for example, by dissolving the
silicone resin and the like in a solvent to prepare a coating solution,
uniformly coating the surface of the core with the coating solution by a
known coating method, drying the applied coating solution and then baking
the surface. Examples of the coating method include immersion coating
method, spray coating method and brush-coating method.

[0242]The solvent is not particularly limited and may be suitably selected
in accordance with the intended use, and examples thereof include
toluene, xylene, methylethylketone, methylisobutylketone, cellosolve and
butyl acetate.

[0243]The backing method is not particularly limited and may be an
external heating method or an internal heating method. Examples thereof
include methods using a fixed type electric furnace, a flowing-type
electric furnace, a rotary electric furnace or a burner furnace or the
like, and methods using a microwave.

[0244]The amount of the resin layer in the carrier is preferably 0.01% by
mass to 5.0% by mass. When the amount of the resin layer is less than
0.01% by mass, the resin layer may not be uniformly formed on the core
surface, and when more than 5.0% by mass, granulation of carrier
particles occurs due to the excessively thick resin layer and a uniform
carrier particle may not be obtained.

[0245]When the developer is a two-component developer, the content of the
carrier in the two-component developer is not particularly limited and
may be suitably adjusted in accordance with the intended use. For
example, it is preferably 90% by mass to 98% by mass and more preferably
93% by mass to 97% by mass.

[0246]Generally, the mixture ratio of the toner to the carrier in the
two-component developer is preferably 10.0 parts by mass of the toner to
100 parts by mass to the carrier.

(Image Forming Apparatus and Image Forming Method)

[0247]The image forming apparatus of the present invention has at least a
latent electrostatic image bearing member, a charging unit, an exposing
unit, a developing unit, a transfer unit and a fixing unit, has a
cleaning unit and further has suitably selected other units in accordance
with necessity, for example, a charge eliminating unit, a recycling unit
and a controlling unit. A combination of a charging unit with an exposing
unit may be referred to as a latent electrostatic image forming unit.

[0248]The image forming method of the present invention includes at least
a charging step, an exposing step, a developing step, a transferring step
and a fixing step, includes a cleaning step and further includes suitably
selected other steps in accordance with necessity, for example, a charge
eliminating step, a recycling step and a controlling step. A combination
of a charging step with an exposing step may be referred to as a latent
electrostatic image forming step.

[0249]The image forming method of the present invention can be favorably
carried out by using the image forming apparatus of the present
invention, the charging step can be carried out using the charging unit,
the exposing step can be carried out using the exposing unit, the
developing step can be carried out by the developing unit, the
transferring step can be carried out using the transfer unit, the fixing
step can be carried out using the fixing unit, the cleaning step can be
carried out using the cleaning unit, and the other steps can be carried
out by using the other units.

<Latent Static Image Bearing Member>

[0250]The latent electrostatic image bearing member is not particularly
limited as to the material, shape, structure, size and the like, and may
be suitably selected in accordance with the intended use. For the shape
of the latent electrostatic image bearing member, for example, drum
shape, sheet shape and endless belt shape are exemplified. The structure
thereof may be a single-layered structure or multi-layered structure, and
the size thereof can be suitably selected in accordance with the size and
the specifications or the like of the image forming apparatus. Examples
of the material used for the latent electrostatic image bearing member
include inorganic photoconductors composed of amorphous silicon,
selenium, CdS, ZnO or the like; organic photoconductors (OPCs) composed
of polysilane, phthalopolymethine or the like.

[0251]The amorphous silicon photoconductor is formed, for example, by
heating a substrate to 50° C. to 400° C. and forming a
photosensitive layer composed of a-Si on the substrate by vacuum
evaporation method, sputtering method, ion-plating method, heat-CVD
method, optical CVD method, plasma CVD or the like. Of these methods,
plasma CVD method is particularly preferable. Specifically, the following
method is preferable. Specifically, raw material gases are decomposed by
a direct current, a high-frequency wave or a microwave glow discharge and
a photosensitive layer composed of a-Si is formed on a substrate.

[0252]The organic photoconductors (OPCs) are widely used for the following
reasons: (1) optical properties such as a wide light absorptive
wavelength region and the size of light absorption amount, (2) electric
properties such as highly sensitive and stable charge properties, (3)
wide selection range of materials, (4) easy manufacturing, (5) low-cost
performance, and (6) non-toxicity. The layer structure of such organic
photoconductors is broadly classified into single-layered structure and
multi-layered structure.

[0253]A photoconductor having a single-layered structure has a substrate
and a single-layered photosensitive layer formed on the substrate and
further has a protective layer, an intermediate layer and other layers in
accordance with necessity.

[0254]A photoconductor having a multi-layered structure has a substrate,
and at least a charge generating layer and a charge transporting layer
formed in this order on the substrate and further has a protective layer,
an intermediate layer and other layers in accordance with necessity.

<Charging Step and Charging Unit>

[0255]The charging step is a step in which the surface of a latent
electrostatic image bearing member is charged and is carried out using
the charging unit.

[0256]The charging unit is not particularly limited and may be suitably
selected in accordance with the intended use, as long as it can uniformly
charge the surface of the latent electrostatic image bearing member by
applying a voltage thereto. The charging units are broadly classified
into (1) contact type charging unit configured to charge a latent
electrostatic image bearing member in a contact manner, and (2)
non-contact type charging unit configured to charge a latent
electrostatic image bearing member in a non-contact manner.

--Contact Type Charging Unit--

[0257]Examples of the (1) contact type charging unit include conductive or
semi-conductive charging rollers, magnetic brushes, fur brushes, films
and rubber blades. Of these, charging rollers are preferred because a
charge roller allows for substantially reduce ozone generation amount as
compared to corona discharge type chargers, is excellent in storage
stability even when a latent electrostatic image bearing member is
repetitively used and is effective to prevent image degradation.

[0258]The magnetic brush is composed, for example, of a non-magnetic
conductive sleeve that bears various ferrite particles such as Zn--Cu
ferrite and a magnet roller that is incorporated into the sleeve. The fur
brush is formed, for example, by twisting or pasting a conduction-treated
fur with carbon, copper sulfide, metal, metal oxide or the like around a
conduction-treated cored bar.

[0259]Here, FIG. 1 is a cross-sectional view showing one example of a
charging roller. A charging roller 310 has a cored bar 311 which is a
cylindrical and serves as a conductive substrate, a resistance
controlling layer 312 formed on the outer circumferential surface of the
cored bar 311 and a protective layer 313 which covers the surface of the
resistance controlling layer 312 to prevent leakage.

[0260]The resistance controlling layer 312 can be formed by extrusion
molding a thermoplastic resin composition containing at least a
thermoplastic resin and a high-molecular weight ion conductive agent on
the circumferential surface of the cored bar 311.

[0261]The volume resistivity value of the resistance controlling layer 312
is preferably 106 Ωcm to 109 Ωcm. When the volume
resistivity value is more than 109 Ωcm, the charged amount is
insufficient and it may be impossible for a photoconductor drum to obtain
such a sufficient charge potential enough to form an image without
causing nonuniformity, and when the volume resistivity value is less than
106 Ωcm, leakage possibly occurs over the whole of the
photoconductor drum.

[0262]The thermoplastic resin used for the resistance controlling layer
312 is not particularly limited and may be suitably selected in
accordance with the intended use. Examples thereof include polyethylene
(PE), polypropylene (PP), methyl polymethacrylate (PMMA), polystyrene
(PS) or copolymers thereof (such as AS and ASB).

[0263]For the high-molecular weight ion conductive agent, an ion
conductive agent that has a resistivity value of about 106 Ωcm
to 1010 Ωcm alone and is capable of easily reducing the
resistance value of the resin is used. For one example thereof, a
compound containing a polyether ester amide component is exemplified. To
control the resistance value of the resistance controlling layer 312 to a
value within the above-noted range, the blending amount of the compound
containing a polyether ester amide component is preferably 30 parts by
mass to 70 parts by mass to 100 parts by mass of the thermoplastic resin.

[0264]Further, as the high-molecular weight ion conductive agent, it is
also possible to use a high-molecular weight compound containing a
quaternary ammonium base. For the high-molecular weight compound
containing a quaternary ammonium base, for example, a polyolefin
containing a quaternary ammonium base is exemplified.

[0265]To control the resistance value of the resistance controlling layer
312 to a value within the above-noted range, the blending amount of the
polyolefin containing a quaternary ammonium base is preferably 10 parts
by mass to 40 parts by mass to 100 parts by mass of the thermoplastic
resin.

[0266]The high-molecular weight ion conductive agent can be dispersed in
the thermoplastic resin by using a biaxial kneader, a kneader or the
like. Because the high-molecular ion conductive agent can be uniformly
dispersed in a thermoplastic resin composition at a molecular level,
variations in resistance value associated with a dispersion defect of the
conductive material, which can be seen in a resistance controlling layer
with a conductive pigment dispersed therein, do not occur in the
resistance controlling layer 312. Further, since the high-molecular
weight ion conductive agent is a polymer compound, it can be uniformly
dispersed and fixed in the thermoplastic resin composition, and bleed-out
hardly occurs.

[0267]The protective layer 313 is formed so as to have a greater
resistance value than that of the resistance controlling layer 312. With
this configuration, leakage to defective parts of the photoconductor drum
can be avoided. However, when the protective layer 313 has an excessively
high resistance value, the charge efficiency is lowered, and thus the
difference in resistance value between the protective layer 313 and the
resistance controlling layer 312 is preferably 103 Ωcm or
less.

[0268]For material used for the protective layer 313, a resin material is
preferable in terms of its excellent formability. For the resin material,
for example, fluorine resins, polyamide resins, polyester resins,
polyvinyl acetal resins are preferable from the perspective of excellence
in non-adhesiveness and capability of preventing toner adhesion. Further,
because a resin material generally has electric insulation prosperities,
properties of the charging roller are not satisfied when the protective
layer 313 is formed with a resin material alone. Then, by dispersing
various conductive agents in the resin material, the resistance value of
the protective layer 313 is controlled. To improve adhesion property
between the protective layer 303 and the resistance controlling layer
302, a reactive curing agent such as isocyanate may be dispersed in the
resin material.

[0269]The charging roller 310 is connected to a light source and a given
voltage is applied thereto. The voltage may be only a direct current (DC)
voltage, however, it is preferable to use a voltage in which an
alternative current (AC) voltage is superimposed on a direct current (DC)
voltage. By applying an AC voltage to the charging roller 310, the
surface of the photoconductor drum can be uniformly charged.

[0270]Here, FIG. 2 is a schematic view showing one example of using a
contact type charging roller i.e., the charge roller 310 as shown in FIG.
1, as a charging unit in an image forming apparatus. In FIG. 2, around a
photoconductor drum 321 serving as a latent electrostatic image bearing
member, a charging unit 310 configured to charge the surface of the
photoconductor drum 321, an exposing unit configured to expose the
charged surface of the photoconductor drum 321 to form a latent
electrostatic image, a developing unit 324 configured to develop the
latent electrostatic image on the photoconductor drum surface by making a
toner adhered on the latent electrostatic image to form a visible image,
a transfer unit 325 configured to transfer the visible image formed on
the photoconductor drum 321 onto a recording medium 326, a fixing unit
327 configured to fix the transferred image on the recording medium 326,
a cleaning unit 330 configured to clean the surface of the photoconductor
drum 321 and collect a residual toner remaining on the photoconductor
drum 321 by removing the residual toner, and a charge eliminating device
331 configured to eliminate a residual potential on the photoconductor
drum 321 are arranged. For the charging unit 310, a contact type charging
roller 310 as shown in FIG. 1 is provided, and the surface of the
photoconductor drum 321 is uniformly charged by the charging roller 310.

--Non-Contact Type Charging Unit--

[0271]For the (2) non-contact type charging unit, for example, a
non-contact type charger utilizing a corona discharge, a needle electrode
device, a solid discharge devices; and a conductive or semi-conductive
charging roller placed with a minute gap to a latent electrostatic image
bearing member are exemplified.

[0272]The corona discharge is a charging method in which a positive or
negative ion generated by a corona discharge in the air is given to the
surface of a latent electrostatic image bearing member. The corona
discharge chargers are classified into corotoron chargers having a
characteristic that a constant charge amount is given to a latent
electrostatic image bearing member, and scorotoron charges having a
characteristic that a constant electric potential is given to a latent
electrostatic image bearing member.

[0273]The corotoron charger is composed of casing electrodes occupying the
half-space thereof around a discharge wire which is positioned roughly in
the center of the casing electrodes.

[0274]The scorotoron charger is a charger of which grid electrodes are
added to the corotoron charger, and the grid electrodes are positioned
1.0 mm to 2.0 mm away from the surface of a latent electrostatic image
bearing member.

[0275]Here, FIG. 3 is a schematic view showing one example of using a
non-contact type corona charger as a charging unit in an image forming
apparatus. Note that in FIG. 3, the same components as shown in FIG. 2
are denoted at the same numerals.

[0276]For the charging unit, a non-contact type corona charger 311 is
provided, and the surface of a photoconductor drum 321 is uniformly
charged by the corona charger 311.

[0277]For the above-noted charging roller placed with a minute gap to a
latent electrostatic image bearing member, the charging roller is
remodeled so as to have a minute gap to the latent electrostatic image
bearing member. The minute gap formed therebetween is preferably 10 μm
to 200 μm and more preferably 10 μm to 100 μm.

[0278]Here, FIG. 4 is a schematic view showing one example of a
non-contact type charging roller. In FIG. 4, a charging roller 310 is
placed with a minute gap H to a photoconductor drum 321. The minute gap
can be set, for example, by twisting a spacer member having a certain
thickness around non-image forming areas in both ends of the charging
roller 310 to make the surface of the spacer member contact with the
surface of the photoconductor drum 321. In FIG. 4, a reference numeral
304 denotes a light source.

[0279]In FIG. 4, as a method of maintaining a minute gap H, a film 302 is
twisted around both ends of the charging roller 310 to form a spacer
member. A spacer 302 is to be made contact with the photosensitive
surface of the latent electrostatic image bearing member and is formed so
as to ensure a certain length of minute gap H between the charging roller
and image areas in the latent electrostatic image bearing member. For the
application bias, an alternative current (AC) superimposing type voltage,
and the latent electrostatic image bearing member is charged by an effect
of an electric discharge generated in the minute gap H between the
charging roller and the latent electrostatic image bearing member. As
shown in FIG. 4, the maintaining accuracy of the minute gap H can be
improved by pressurizing a charging roller axis 311 with a spring 303.

[0280]The spacer member may be combined with a charging roller to
integrally form one unit. In this case, at least the surface of the gap
portion must be formed of an insulating material. With this, it is
possible to reduce an electric discharge at the gap portion and to
prevent an electric discharge product from accumulating at the gap
portion, to prevent a toner from being fixed to the gap portion due to
surface tackiness of the electric discharge product, and to prevent the
gap from outspreading.

[0281]For the spacer member, a heat shrinkable tube may be used. Examples
of such a heat shrinkable tube include SUMITUBE for 105° C.
(product name: F105° C., manufactured by Sumitomo Chemical Co.,
Ltd.).

<Exposing Step and Exposing Unit>

[0282]The exposing step is a step in which the charged surface of the
latent electrostatic image bearing member is exposed by using the
exposing unit.

[0283]The exposure can be carried out, for example, by exposing the
surface of the latent electrostatic image bearing member imagewisely
using the exposing unit.

[0284]Optical systems to be used for the exposure are broadly classified
into analogue optical systems and digital optical systems. The analogue
optical system is the one that directly projects an original document on
a latent electrostatic image bearing member from an optical system, and
in the digital optical system, image information is given as electrical
signals, the electrical signals are converted into optical signals, a
latent electrostatic image bearing member is exposed to thereby form an
image.

[0285]The exposing unit is not particularly limited and may be suitably
selected in accordance with the intended use, as long as it can
imagewisely expose the latent electrostatic image bearing member surface
that has been charged by the charging unit. Examples of the exposing unit
include reproducing optical systems, rod lens array systems, laser
optical systems, liquid crystal shutter optical systems and LED optical
systems.

[0286]In the present invention, the back light method may be employed in
which exposure is performed imagewisely from the back side of the
photoconductor.

<Developing Step and Developing Unit>

[0287]The developing step is a step in which the latent electrostatic
image is developed using the toner of the present invention or the
developer to form a visible image by means of the developing unit.

[0288]The developing unit is not particularly limited and may be suitably
selected from among conventional developing units, as long as it can
develop a latent electrostatic image using a toner or a developer. For
example, a developing unit having at least a developing device which
houses the toner or the developer and supplies the toner or the developer
to the latent electrostatic image in a contact or non-contact manner is
preferably exemplified.

[0289]The developing device may employ a dry-developing process or a
wet-developing process. It may be a monochrome color image developing
device or a multi-color image developing device. Preferred examples
thereof include a developing device having a stirrer by which the toner
or the developer is frictionally stirred to be charged, and a rotatable
magnet roller.

[0290]In the developing device, for example, the toner and a carrier are
mixed and stirred, the toner is charged by a frictional force at that
time to be held in a state where the toner is standing on the surface of
the rotating magnet roller to thereby form a magnetic brush. Because the
magnet roller is located near the latent electrostatic image bearing
member, a part of the toner constituting the magnetic brush formed on the
surface of the magnet roller moves to the surface of the latent
electrostatic image bearing member by an electric attraction force. As
the result, the latent electrostatic image is developed using the toner
to form a visible toner image on the surface of the latent electrostatic
image bearing member.

[0291]A developer to be housed in the developing unit is a developer
containing the toner, however, the developer may be a one-component
developer or a two-component developer.

[One-Component Developing Unit]

[0292]For the one-component developing unit, for example, a one-component
developing device having a developer carrier to which a toner is supplied
and a layer thickness controlling member that forms a toner thin layer on
the surface of the developer carrier is preferably used.

[0293]FIG. 5 is a schematic view showing one example of a one-component
developing device. In the one-component developing device, a
one-component developer composed of only a toner is used. The
one-component developing device allows for developing a latent
electrostatic image on a photoconductor drum 1 using the one-component
developer in a contact manner by forming a toner layer on a developing
roller 402 as a developer carrier and conveying the toner layer on the
developing roller 401 so as to make contact with the photoconductor drum
1.

[0294]In FIG. 5, a toner in a casing 401 is stirred by rotation of an
agitator 411 as an agitating unit and is mechanically supplied to a
supplying roller 412 as a toner supplying member. The supplying roller
412 is formed of foamed polyurethane or the like and has flexibility and
a cell diameter of 50 μm to 500 μm to be formed in such a structure
to easily hold a toner on the surface thereof. The JIS-A hardness of the
supplying roller 412 is relatively low of 10° to 30°, and
thus it can be made evenly contact with the developing roller 402 as
well.

[0295]The supplying roller 412 is driven to rotate in the same direction
as the developing roller 402 rotates, i.e., the supplying roller 412 is
driven to rotate such that the surface of the supplying roller 412 and
the surface of the developing roller 402 rotate and move in the opposite
direction from each other at the portion where both of the rollers face
to each other. A linear speed ratio of the supplying roller to the
developing roller (supplying roller/developing roller) is preferably 0.5
to 1.5. Also, the supplying roller 412 may be driven to rotate in the
opposite direction from the direction in which the developing roller 402
rotates, i.e., may be driven to rotate such that the surface of the
supplying roller 412 and the surface of the developing roller 402 rotate
and move in the same direction with each other at the portion where both
of the rollers face to each other. In this embodiment, the supplying
roller 412 was set so as to rotate in the same direction as the
developing roller 402 rotates, and the linear speed ratio was set to 0.9.
The biting amount of the supplying roller 412 into the developing roller
402 was set to 0.5 mm to 1.5 mm. In this embodiment, when the unit
effective width is 240 mm (A4 size, vertical), a necessary torque is 14.7
Ncm to 24.5 Ncm.

[0296]The developing roller 402 has a surface layer composed of a rubber
material on a conductive substrate and has a diameter of 10 mm to 30 mm.
The surface thereof is roughly formed so as to have a surface roughness
Rz of 1 μm to 4 μm. The surface roughness Rz is preferably set at
13% to 80% to the average particle diameter of the toner. With this
configuration, the toner is conveyed without being embedded in the
surface of the developing roller 402. Particularly, the surface roughness
Rz of the developing roller 402 is preferably controlled to be a value
ranging 20% to 30% of the average particle diameter of the toner so as
not to hold a significantly low-charge toner on the surface of the
developing roller 402.

[0297]Examples of the rubber material include silicone rubbers, butadiene
rubbers, NBR rubbers, hydrin rubbers and EPDM rubbers. Further, it is
preferable to coat the surface of the developing roller 402 with a
coating layer to stability the quality with time, particularly. Examples
of material used for the coating layer include silicone materials, TEFLON
(registered) materials. The silicone materials are excellent in toner
charging property, and the TEFLON (registered) materials are excellent in
releasing property. To obtain conductivity, a conductive material such as
carbon black may be suitably added to the coating layer. The thickness of
the coating layer is preferably 5 μm to 50 μm. When the thickness
of the coating layer deviates the range, it is likely to cause a problem
that it breaks easily.

[0298]A toner having a specific polarity (in this embodiment, negative
polarity) residing on or inside the supplying roller 412 is sandwiched in
a contact point with the developing roller 402, in the contact point
where the supplying roller 412 and the developing roller 402 rotate in
the opposite direction from each other because of rotation thereof, and
the toner obtains a negatively charged charge by a frictional charging
effect and is then held on the surface of the developing roller 402 by an
electrostatic force and a conveying effect of the surface roughness of
the developing roller 402. A toner layer formed on the developing roller
402 at this point in time is not uniformly formed and an excessive amount
of toner adheres thereon (1 mg/cm2 to 3 mg/cm2). To solve the
problem, a controlling blade 413 as a layer thickness controlling member
is made contact with the developing roller, thereby forming a toner thin
layer having a uniform thickness on the developing roller 402. The
controlling blade 413 is placed so that the tip of the controlling blade
413 faces the downstream of the rotational direction of the developing
roller 402 and the center part of the controlling blade 413 makes contact
with the developing roller 402. This state is generally called a belly
contact state, however, it is also possible to set the tip in the
opposite direction from the above-noted direction, and also possible to
set the controlling blade 413 in an edge contact state.

[0299]Material used for the controlling blade 413 is preferably metal such
as SUS304, the thickness is ranging from 0.1 mm to 0.15 mm. Besides
metals, a rubber material such as polyurethane rubber, having a thickness
of 1 mm to 2 mm, and a resin material having a relatively high hardness
such as silicone resin are usable. Even with the use of a material other
than metal, it is possible to form a controlling blade having a
low-resistivity by mixing carbon black in the material, and thus it is
also possible to form an electric field in between the controlling blade
413 and the developing roller 402 by connecting the controlling blade 413
to a bias light source.

[0300]The controlling blade 413 serving as the layer thickness controlling
member preferably has a free end length of 10 mm to 15 mm from a holder
thereof. When the free end length is longer than 15 mm, it results in a
large size developing unit, and it is impossible to compactly install the
developing unit in an image forming apparatus. When the free end length
is shorter than 10 mm, it is likely to cause vibration when the
controlling blade 413 makes contact with the surface of the developing
roller 402, and abnormal images such as image nonuniformity in lateral
tiers easily occur on images.

[0301]The contact pressure of the controlling blade 413 is preferably
ranging from 0.049 N/cm to 2.45 N/cm. When the contact pressure is more
than 2.45 N/cm, the amount of the toner adhered on the developing roller
402 is reduced and the toner charge amount excessively increases, and
therefore, the developing amount is decreased and the image density may
be reduced. When the contact pressure is less than 0.049 N/cm, a thin
layer is not uniformly formed, a toner agglomerate may pass by the
controlling blade 413, and the image quality may be significantly
degraded. In this embodiment, for the developing roller 402, a developing
roller having a JIS-A hardness of 30° was used, for the
controlling blade 413, a SUS plate of 0.1 mm in thickness was used, and
the contact pressure was set to 60 gf/cm. In this case, an intended toner
adhesion amount could be obtained on the developing roller 402.

[0302]The contact angle of the controlling blade 413 as a layer thickness
controlling member formed with a tangent line of the developing roller
402, in the direction where the tip of the controlling blade 413 faces
the downstream of the developing roller 402, is preferably 10° to
45°. A toner amount of the toner not required to form a toner thin
layer sandwiched in between the controlling blade 413 and the developing
roller 402 is striped off from the developing roller 402, and then it is
possible to form a thin layer having a uniform thickness of a weight per
unit area of 0.4 mg/cm2 to 0.8 mg/cm2, which is within the
target range. In this embodiment, the charged amount of the toner at this
point in time is within the range of -10 μC/g to -30 μC/g, and the
toner is developed at a position that faces the latent electrostatic
image on the photoconductor drum 1.

[0303]Therefore, with the use of the one-component developing device of
the embodiment, the distance between the surface of the photoconductor
drum 1 and the surface of the developing roller 402 becomes narrower than
that in a conventional two-component developing unit, and the developing
ability is increased to allow for developing even with a lower electric
potential.

(Two Component Developing Unit)

[0304]For the two-component developing unit, a two component developing
device is preferable which has a magnetic field generating unit fixed
inside thereof and a developer carrier that carries a two component
developer containing a magnetic carrier and a toner and is rotatable.

[0305]Here, FIG. 6 is a schematic view showing one example of a two
component developing device using a two component developer which
contains a toner and a magnetic carrier. In the two component developing
device shown in FIG. 6, a two component developer is stirred and conveyed
by a screw 441 and supplied to a developing sleeve 442 serving as a
developer carrier. The two component developer supplied to the sleeve 442
is controlled by a doctor blade 443 serving as a layer thickness
controlling member, and the supplied amount of the developer is
controlled by a doctor gap which is an interval between the doctor blade
443 and the developing sleeve 442. When the doctor gap is excessively
small, the image density becomes insufficient due to an excessively small
amount of the developer. In contrast, when the doctor gap is excessively
large, the amount of the developer is excessively supplied thereto, which
causes a problem that the carrier adheres on a photoconductor drum 1
serving as a latent electrostatic image bearing member. To prevent this
problem, inside the developing sleeve 442, a magnet is provided which
serves as a magnetic field generating unit configured to form a magnetic
field so that the developer is standing on the circumferential surface.
Then, the developer stands chain-likely on the developing sleeve 442
along magnetic field lines in normal line which are generated from the
magnetic to thereby form a magnetic brush.

[0306]The developing sleeve 442 and the photoconductor drum 1 are disposed
so as to closely contact each other with a certain space (developing gap)
therebetween, and a developing region is formed at a position where both
the developing sleeve 442 and the photoconductor drum 1 face to each
other. The developing sleeve 442 is made of a non-magnetic material such
as aluminum, brass, stainless steel, and conductive resin and is formed
in a cylindrical shape and is driven to rotate by a revolution drive
mechanism (not shown). The magnetic brush is conveyed to the developing
region by rotation of the developing sleeve 442. To the developing sleeve
442, a developing voltage is applied from a developing light source (not
shown), a toner on the magnetic brush is separated from the carrier by a
developing electric field formed between the developing sleeve 442 and
the photoconductor drum 1 and developed on a latent electrostatic image
on the photoconductor drum 1.

[0307]The size of the developing gap is preferably 5 times to 30 times the
particle diameter of the developer. When the particle diameter of the
developer is 50 μm, it is preferable that the developing gap be set to
0.5 mm to 1.5 mm. A developing gap wider than 1.5, desired image density
may be rarely obtained.

[0308]The doctor gap is preferably as large as the developing gap or
slightly larger than the developing gap. The drum diameter and drum
linear speed of the photoconductor drum 1 and the sleeve diameter and the
sleeve linear speed of the developing sleeve 442 are determined depending
on restrictions such as copying speed and size of an image forming
apparatus used. The ratio of the sleeve linear speed to the drum linear
speed is preferably set to 1.1 or more to obtain necessary image density.
Further, processing conditions can be controlled by installing a sensor
at a position that has gone through developing and detecting the toner
adhesion amount from optical reflectance.

<Transferring Step and Transfer Unit>

[0309]The transferring step is a step in which the visible image is
transferred onto a recording medium by using a transfer unit. The
transfer unit is broadly classified into a transfer unit configured to
directly transfer a visible image on a latent electrostatic image bearing
member onto a recording medium, and a secondary transfer unit configured
to primarily transfer a visible image on an intermediate transfer member
and then secondarily transfer the visible image onto a recording medium.

[0310]The transferring can be accomplished by charging the latent
electrostatic image bearing member using a transfer-charger by means of
the transfer unit. For the transfer unit, an aspect of the transfer unit
is preferable which has a primary transfer unit configured to transfer a
visible image on an intermediate transfer member to form a complex
transfer image and a secondary transfer unit configured to transfer the
complex transfer image onto a recording medium.

--Intermediate Transfer--

[0311]The intermediate transfer member is not particularly limited and may
be suitably selected from among conventional transfer members in
accordance with the intended use. Preferred examples thereof include
transfer belts and transfer rollers.

[0312]The static friction coefficient of the intermediate transfer member
is preferably 0.1 to 0.6 and more preferably 0.3 to 0.5. The volume
resistivity of the intermediate transfer member is preferably several
ohm-centimeters to 10 Ωcm. By adjusting the volume resistivity of
the intermediate transfer member to several ohm-centimeters to 10
Ωcm, it is possible to prevent the intermediate transfer member
itself being charged and a charge given to a charge providing unit rarely
remain on the intermediate transfer member, and thus transfer
nonuniformity at the time of secondary transfer can be prevented. Also, a
transfer bias can be easily applied at the time of secondary transfer.

[0313]Material used for the intermediate transfer member is not
particularly limited and may be suitably selected from among conventional
materials in accordance with the intended use, however, the following
materials are preferably used.

[0314](1) Materials with a high Young's modulus (tension elasticity) used
as a single layer belt. Examples thereof includes polycarbonates (PC),
polyvinylidene fluoride (PVDF), polyalkylene terephthalate (PAT), blend
materials of PC/PAT, ethylene tetrafluoroethylene copolymer (ETFE)/PC,
and ETFE/PAT, and thermosetting polyimides of carbon black dispersion.
These single layer belts having a high Young's modulus are small in their
deformation against stress during image formation and are particularly
advantageous in that misalignment of rib does not easily occur when
forming a color image.

[0315](2) A double or triple layer belt using the above-noted belt having
a high Young's modulus as a base layer, formed with a surface layer and
an optional intermediate layer around the peripheral surface of the base
layer. The double or triple layer belt has a capability to prevent print
defect of unclear center portion in a line image that is caused by the
hardness of the single layer belt.

[0316](3) A belt with a relatively low Young's modulus formed by using a
rubber or an elastomer. This belt has an advantage that there is almost
no print defect of unclear center portion in a line image due to its
softness. Additionally, by making the width of the belt wider than
driving and tension rollers and thereby using the elasticity of the edge
portions that extend over the rollers, it can prevent snaky move of the
belt. Therefore, it can reduce cost without the need for ribs and a
device to prevent the snaky move.

[0317]Of these belts, the (3) elastic belt is particularly preferable.

[0318]The elastic belt becomes deformed, in a transfer portion, according
to the surface form of a toner layer and/or a recording medium which is
poor in surface smoothness. In other words, since such an elastic belt is
deformed, following local convexoconcaves or irregularities, it is
possible to obtain excellent adhesiveness without excessively increasing
a transfer pressure to a toner layer and to obtain a transfer image which
is excellent in uniformity without causing print defect of unclear center
portion in a line image even on a recording medium which is poor in
surface planality.

[0321]Elastomer used for the elastic belt is not particularly limited and
may be suitably selected in accordance with the intended use. Examples
thereof include polystyrene thermoplastic elastomers, polyolefin
thermoplastic elastomers, polyvinyl chloride thermoplastic elastomers,
polyurethane thermoplastic elastomers, polyamide thermoplastic
elastomers, polyurea thermoplastic elastomers, polyester thermoplastic
elastomers and fluorine thermoplastic elastomers. Each of these
elastomers may be used alone or in combination with two or more.

[0322]A conductive agent for controlling resistivity used for the elastic
belt is not particularly limited and may be suitably selected in
accordance with the intended use. Examples thereof include metal powders
of carbon black, graphite, aluminum, nickel and the like; and conductive
metal oxides such as tin oxide, titanium oxide, antimony oxide, indium
oxides, potassium titanate, antimony oxide-tin oxide composite oxide
(ATO) and indium oxide-tin oxide composite oxide (ITO). For the
conductive metal oxide, the one coated with an insulating fine particle
such as barium sulfate, magnesium silicate and calcium carbonate may be
used.

[0323]For the surface layer of the elastic belt, such a layer that allows
for preventing contamination from an elastic material to a latent
electrostatic image bearing member, reducing frictional resistance of a
belt surface to reduce the toner-adhesive force and improving cleaning
ability and secondary transfer properties is preferable. It is preferable
that the surface layer contain a binder resin such as polyurethane resin,
polyester resin and epoxy resin, and a material that can reduce the
surface energy and increase the lubricating property of the surface
layer, for example, a powder or a particle of fluorine resin, fluorine
compound, fluorocarbon, titanium dioxide, silicon carbide or the like.
Further, the surface layer may be a fluorine-rich surface layer which is
heat-treated like fluorine rubber material to thereby reduce the surface
energy.

[0324]A method of producing the elastic belt is not particularly limited
and may be suitably selected in accordance with the intended use. The
following methods are exemplified. Specifically, (1) centrifugal forming
method in which a material is poured into a rotating cylindrical die,
thereby forming a belt, (2) spray coating method in which a liquid
coating material is sprayed to form a film, (3) dipping method in which a
cylindrical die is dipped in a solution and then lifted therefrom, (4)
casting method in which a material is poured into an inner die or an
outer die, and (5) a method in which a compound is twisted around a
cylindrical die and the surface is vulcanized and polished.

[0325]A method of preventing extension or stretch of the elastic belt is
not particularly limited and may be suitably selected in accordance with
the intended use. The following methods are exemplified. For example, (1)
a method of adding a material capable of preventing extension or stretch
to a core layer, and (2) a method of forming a rubber layer on a core
layer that is less extensible or stretchable.

[0327]A method of forming the core layer is not particularly limited and
may be suitably selected in accordance with the intended use. The
following methods are exemplified. For example, (1) a method in which a
die etc. is covered with a fabric woven into a tube-shape, and a coating
layer is formed on the die, (2) a method in which a fabric woven into a
tube-shape is immersed in a liquid rubber etc., and a coating layer is
formed on one surface or both surfaces of the core layer, and (3) a
thread is spirally twisted around a die etc. at an arbitrarily determined
pitch, and a coating layer is formed on the die.

[0328]When the coating layer is excessively thick, stretchability of the
surface is increased to easily cause cracks on the surface layer,
although it depends on the hardness of the coating layer. It is not
preferred to use an excessively thick coating layer having a thickness of
about 1 mm or more because the stretched amount will be large, resulting
in large amount of extension and shrinkage of image.

[0329]It is preferable that the transfer units (the primary transfer unit
and the secondary transfer unit) have at least an image transfer device
capable of peeling off and charging the visual image formed on the latent
electrostatic image bearing member and transferring it onto a recording
medium. One image transfer device or two or more image transfer devices
may be used. Examples of the image transfer device include corona image
transfer device utilizing corona discharge, transfer belts, transfer
rollers, pressure-transfer rollers and tacky image transfer devices.

[0330]For a recording medium, regular paper is typically used, however, it
is not particularly limited and may be suitably selected in accordance
with the intended use, as long as it can transfer unfixed images after
developing process. PET-base materials for OHP can also be used.

--Transfer Unit for Tandem-Type Image Forming Apparatus--

[0331]In the tandem-type image forming apparatus, at least a plurality of
elements including latent electrostatic image bearing members, charging
units, developing units and transfer units are arrayed. In the
tandem-type image forming apparatus, four image forming sections of
yellow, magenta, cyan and black therein are installed therein, individual
color visual images are produced using the four image forming sections in
parallel, and the color visual images are superimposed on a recording
medium or an intermediate transfer member, and thus it can form a
full-color image at higher speed.

[0332]For the tandem-type image forming apparatus, there are the following
type apparatuses: (1) as shown in FIG. 7, a direct-transfer type image
forming apparatus, in which visual images formed on respective latent
electrostatic image bearing members 1 are sequentially transferred by
means of transfer units 2 onto a recording medium S whose surface moves
so as to pass a transfer position that faces the respective latent
electrostatic image bearing members 1 in a plurality of image forming
sections; and (2) as shown in FIG. 8, an indirect-transfer type image
forming apparatus, in which visual images formed on respective latent
electrostatic image bearing members 1 in a plurality of image forming
sections are sequentially transferred on an intermediate transfer member
4 once by transfer units (primary transfer units) 2, and then the images
on the intermediate transfer member 4 are transferred onto a recording
medium S at a time by a secondary transfer unit 5. Note that in FIG. 8, a
transfer conveying belt is used as the secondary transfer unit, however,
it may be formed in a roller shape.

[0333]When the (1) direct-transfer type image forming apparatus is
compared with the (2) indirect-transfer type image forming apparatus, in
the (1) direct-transfer type image forming apparatus, a sheet feeder 6
must be placed upstream of a tandem-type image forming section T and a
fixing device 7 must be placed downstream of the tandem-type image
forming section T, and thus the image forming apparatus must be made in a
large size in the recording medium conveying direction. In contrast, the
(2) indirect-transfer type image forming apparatus is advantageous in
that a secondary transfer position is relatively freely located, a sheet
feeder 6 and a fixing device 7 can be vertically arrayed with a
tandem-type image forming section T and it allows for compactness in
size.

[0334]Further, in the (1) direct-transfer type image forming apparatus, to
avoid making the apparatus large in size in the recording medium
conveying direction, it is necessary to place the fixing device 7 close
to the tandem-type image forming section T. Therefore, it is impossible
to place the fixing device 7 with a sufficient margin where the recording
medium S can sag, and the fixing device 7 easily affects image formation
upstream thereof due to an impact given when one end of the recording
medium S enters the fixing device 7 (particularly conspicuous with a
thick recording medium), a speed difference between the conveying speed
of the recording medium S at the time of passing through the fixing
device 7 and the conveying speed of the recording medium S by means of
the transfer conveying belt. In contrast, since the (2) indirect-type
transfer image forming apparatus allows for installation of the fixing
device 7 with a sufficient margin where the recording medium S can sag,
the fixing device 7 rarely affect image formation.

[0335]For the above noted reasons, recently, indirect-transfer type image
forming apparatuses have become a focus of attention, particularly. In
such a color image forming apparatus, as shown in FIG. 8, a transfer
residual toner remaining on the surface of the latent electrostatic image
bearing members 1 after primary transfer is removed using cleaning
devices 8 as cleaning units to thereby clean the respective surfaces of
the latent electrostatic image bearing members 1 and provide for next
image formation. Further, a transfer residual toner remaining on the
intermediate transfer member 4 after secondary transfer is removed using
an intermediate transfer member cleaning device 9 to thereby clean the
surface of the intermediate transfer member 4 and provide for next image
formation.

<Fixing Step and Fixing Unit>

[0336]The fixing step is a step in which the transferred visual image is
fixed on a recording medium using a fixing unit.

[0337]The fixing unit is not particularly limited and may be suitably
selected in accordance with the intended use, however, a fixing device
having a fixing member and a heat source to heat the fixing member is
preferably used.

[0338]The fixing member is no particularly limited and may be suitably
selected in accordance with the intended use, as long as a pair of
members can make contact with each other to form a nip portion. Examples
of thereof include a combination of an endless belt and a roller and a
combination of a roller and another roller. It is preferable to use a
combination of an endless belt and a roller or to use a heating method of
heating from the surface of the fixing member by induction heating, etc.,
in terms of capability of shortening warm-up time and achievement of
energy-saving.

[0339]Examples of the fixing member include conventional
heating-pressurizing units (a combination of a heating unit and a
pressurizing unit) are exemplified. For the heating-pressurizing unit, in
the case of a combination of an endless belt and a roller, for example, a
combination of a heating roller, a pressurizing roller and an endless
belt is exemplified. In the case of a combination of a roller and another
roller, for example, a combination of a heating roller and a pressurizing
roller is exemplified.

[0340]When the fixing member is an endless belt, the endless belt is
preferably formed with a material having small heat capacity. For
example, an aspect in which an offset-preventing layer is formed on a
base is exemplified. Examples of material used for forming the base
include nickels and polyimides. For material used to form the
offset-preventing layer, silicone rubbers and fluorine resins are
exemplified.

[0341]When the fixing member is a roller, the cored bar of the roller is
preferably formed with a non-elastic member to prevent deformation
(flexure) that could be caused by high-pressure. Material used for the
non-elastic member is not particularly limited and may be suitably
selected in accordance with the intended use. Preferred examples thereof
include high-thermal conductive materials such as aluminum, iron,
stainless steel and brass. Further, the roller is preferably covered with
an offset-preventing layer. Material used to form the offset-preventing
layer is not particularly limited and may be suitably selected in
accordance with the intended use. Examples thereof include RTV silicone
rubbers, tetrafluoroethylene-perfluoroalkyl vinyl ether (PFA) and
polytetrafluoroethylene (PTFE).

[0342]In the fixing step, an image formed with the toner may be fixed on
the recording medium by transferring the toner image onto the recording
medium and passing the recording medium bearing the image through the nip
portion, or the transferring of the toner image onto the recording medium
and the fixing thereof may be performed at the nip portion at the same
timing.

[0343]The fixing may be performed for each of color toners every time each
of the color toners is transferred to the recording medium, or respective
color-toner images may be fixed at a time in a state where the
color-toner images are superimposed on the recording medium.

[0344]The nip portion is formed by bringing at least two fixing members
into contact with each other.

[0345]The contact pressure of the nip portion is not particularly limited
and may be suitably selected in accordance with the intended use,
however, it is preferably 5 N/cm2 or more, more preferably 7
N/cm2 to 100 N/cm2, and still more preferably 10 N/cm2 to
60 N/cm2. When the contact pressure of the nip portion is
excessively high, the durability of the roller may degrade. When the
contact pressure of the nip portion is less than 5 N/cm2, the offset
resistance may become insufficient.

[0346]The temperature when the toner image is fixed on the recording
medium i.e., the surface temperature of the fixing member from the
heating unit, is not particularly limited and may be suitably selected in
accordance with the intended use, however, it is preferably 120°
C. to 170° C. and more preferably 120° C. to 160° C.
When the fixing temperature is lower than 120° C., the fixing
property may become insufficient, and when higher than 170° C., it
is unfavorable in terms of achievement of energy-saving.

[0347]The fixing unit is broadly classified into the following two types:
(1) an aspect of a fixing unit that has at least one of a roller and a
belt and is configured to fix a transferred image on a recording medium
by heating the transferred image from the surface of at least any one of
the roller and the belt that does not make contact with the toner and
pressurizing the transferred image on the recording medium (internal
heating method), and (2) an aspect of a fixing unit that has at least any
one of a roller and a belt and is configured to fix a transferred image
on a recording medium by heating the transferred image from the surface
of at least any one of the roller and the belt that makes contact with
the toner and pressurizing the transferred image on the recording medium
(external heating method). It is also possible to use a combination of
both of the methods.

[0348]For a fixing unit based on the (1) internal heating method, for
example, the one that the fixing member itself has a heating unit inside
thereof is exemplified. Examples of such a heating unit include heat
sources such as heater and halogen lamp.

[0349]For a fixing unit based on the (2) external heating method, for
example, an aspect is preferable in which at least a part of at least one
surface of the fixing member is heated by a heating unit. Such a heating
unit is not particularly limited and may be suitably selected in
accordance with the intended use. For example, electromagnetic induction
heating units are exemplified.

[0350]The electromagnetic induction heating unit is not particularly
limited and may be suitably selected in accordance with the intended use,
however, an aspect is preferable which has a unit configured to generate
a magnetic field and a heat generating unit configured to generate heat
by electromagnetic induction.

[0351]For the electromagnetic induction heating unit, for example, an
aspect is preferable which has an induction coil located close to the
fixing member (for example, a heating roller), a shielding layer formed
on the induction coil and an insulating layer formed on the opposite
surface of the shielding layer from the surface with the induction coil
formed thereon. In this case, for the heating roller, an aspect is
preferable which is made of a magnet or a heat pipe.

[0352]It is preferable that the induction coil be located at the opposite
side of a contact position between the heating roller and the fixing
member (for example, a pressurizing roller, an endless belt, etc.) in a
condition where the induction coil wraps at least a half cylinder part of
the heating roller.

--Fixing Unit Based on Internal Heating Method--

[0353]FIG. 9 is a belt type fixing device showing one example of a fixing
unit based on internal heating method. A belt type fixing device 510
shown in FIG. 9 is equipped with a heating roller 511, a fixing roller
512, a fixing belt 513 and a pressurizing roller 514.

[0354]The fixing belt 513 is spanned over the heating roller 511 and the
fixing roller 512 that are rotatably located inside the fixing belt 513
and is heated to a predetermined temperature by the heating roller 511.
The heating roller 511 incorporates a heating source 515 inside thereof
and is designed such that temperature is adjustable by a temperature
sensor 517 closely mounted to the heating roller 511. The fixing roller
512 is rotatably located inside the fixing belt 513 while making contact
with the inner surface of the fixing belt 513. The pressurizing roller
514 is rotatably located outside the fixing belt 513 so as to make
contact with the outer surface of the fixing belt 513 with pressure. The
surface hardness of the fixing belt 513 is lower than the surface
hardness of the pressurizing roller 514. In a nip portion N formed
between the fixing roller 512 and the pressurizing roller 514, an
intermediate area positioned between the introduction end of a recording
medium S and the injection end of the recording medium S nearer the
fixing roller 512 than the introduction end and the injection end of the
recording medium S.

[0355]In the belt type fixing device 510 shown in FIG. 9, the recording
medium S with a toner image T to be subjected to a fixing step formed
thereon is conveyed to the heating roller 511. The toner image T on the
recording medium S is heated to a molten state by the heating roller 511
and the fixing belt 513 that are heated to a predetermined temperature by
effect of the heating source 515 that is incorporated into the heating
roller 511. In this state, the recording medium S is inserted into the
nip portion N formed between the fixing roller 512 and the pressurizing
roller 514. The recording medium S inserted into the nip portion N is
made contact with the surface of the fixing belt that is linked with
rotation of the fixing roller 512 and the pressurizing roller 514 to
rotate and is pressured at the time of passing through the nip portion N,
thereby the toner image is fixed on the recording medium S.

[0356]Next, the recording medium S with the toner image T fixed thereon
passes through between the fixing roller 512 and the pressurizing roller
514 and is peeled off from the fixing belt 513 to be conveyed to a tray
(not shown). At that time, the recording medium S is ejected toward the
pressurizing roller 514 to prevent the recording medium S from being
wound around the fixing belt 513. The outer surface of the fixing belt
513 is cleaned by a cleaning roller 516.

[0357]A heat roller type fixing device 515 shown in FIG. 10 is equipped
with a heating roller 520 serving as the fixing member and a pressurizing
roller 530 located so as to make contact with the heating roller 520.

[0358]The heating roller 520 has a hollow metal cylinder 521 and is coated
with an offset prevention layer 522 on the surface thereof, and at the
inner part, a heating lamp 523 is placed. The pressurizing roller 530 has
a metal cylinder 531 and is coated with an offset prevention layer 532 on
the surface thereof. The metal cylinder 531 is formed in a hollow shape,
and at the inner part of the pressurizing roller 530, a heating lamp 533
may be placed. The heating roller 520 and the pressurizing roller 530 are
biased by a spring (not shown), thereby being rotatably provided so as to
contact with pressure each other and form a nip portion N. The surface
hardness of the offset prevention layer 522 in the heating roller 520 is
lower than the surface hardness of the offset prevention layer 532 in the
pressurizing roller 530. In a nip portion N formed between the heating
roller 520 and the pressurizing roller 530, an intermediate area
positioned between the introduction end of a recording medium S and the
injection end of the recording medium S nearer the heating roller 520
than the introduction end and the injection end of the recording medium
S.

[0359]In the heating roller type fixing device 515 shown in FIG. 10,
first, the recording medium S with a toner image T to be subjected to a
fixing step formed thereon is conveyed to the nip portion N between the
heating roller 520 and the pressurizing roller 530. A toner T on the
recording medium S is heated to a molten state by the heating roller 520
that is heated to a predetermined temperature by effect of the heating
lamp 523 that is incorporated into the heating roller 520, and at the
same time, is pressed by a pressing force of the pressurizing roller 530,
thereby a toner image T is fixed on the recording medium S.

[0360]Next, the recording medium S with the toner image T fixed thereon
passes through between the heating roller 520 and the pressurizing roller
530 and is conveyed to a tray (not shown). At that time, the recording
medium S is ejected toward the pressurizing roller 530 to prevent the
recording medium S from being wound around the pressurizing roller 530.
The heating roller 520 is cleaned by a cleaning roller 516.

--Fixing Unit Based on External Heating Method--

[0361]FIG. 11 is an electromagnetic induction heating type fixing device
570 that is exemplarily showing one example of a fixing unit based on
external heating method. The electromagnetic induction heating type
fixing device 57 is equipped with a heating roller 566, a fixing roller
580, a fixing belt 567, a pressurizing roller 590 and an electromagnetic
induction heating unit 560.

[0362]The fixing belt 567 is spanned over the heating roller 566 and the
fixing roller 580 that are rotatably located inside the fixing belt 567
and is heated to a predetermined temperature by the heating roller 566.

[0363]The heating roller 566 is formed, for example, into a hollow
cylindrical shape of a magnetic metal material such as iron, cobalt,
nickel or a metal alloy thereof, and has an eternal diameter of 20 mm to
40 mm and a wall thickness of 0.3 mm to 1.0 mm, and has a structure that
allows for a high-speed temperature increase with low thermal capacity.

[0364]The fixing roller 580 has, for example, a cored bar 581 made of a
stainless steel or the like, and the surface thereof is covered with an
elastic layer 582 that is formed with a silicone rubber having heat
resistance into a solid or foam formation. The fixing roller 580 is
rotatably located while making contact with the inner surface of the
fixing belt 567 inside the fixing belt 567. The fixing roller 580 is
designed to have an external diameter of about 20 mm to 40 mm, which is
larger than the external diameter of the heating roller 566 in order to
form a nip portion N having a predetermined width between the
pressurizing roller 590 and the fixing roller 580 by a pressing force
from the pressurizing roller 590. The elastic layer 582 has a wall
thickness of around 4 mm to 6 mm and is formed such that the thermal
capacity of the heating roller 566 is smaller than the thermal capacity
of the fixing roller 580, thereby shortening the warm-up time of the
heating roller 566.

[0365]The pressurizing roller 590 has a cored bar 591 formed of a
cylindrical member with a metal which has high-thermal conductivity, for
example, copper and aluminum, and the pressurizing roller 590 has a
surface that is covered with an elastic layer 592 having a high-thermal
resistance and high-toner releasing property has is rotatably located on
the outer surface of the fixing belt 567 while contacting with the fixing
roller 580 with pressure. For the cored bar 591, SUS may be used, besides
the above-noted metal materials.

[0366]An electromagnetic induction heating unit 560 is located near the
heating roller 566 and is formed in the axial direction of the heating
roller 566. The electromagnetic induction heating unit 560 has an
exciting coil 561 serving as a magnetic field generating unit and a coil
guide plate 562 around which the exciting coil 561 is wound. The coil
guide plate 562 is formed in a half-cylinder shape and is located closely
to the outer circumferential surface of the heating roller 566. The
exciting coil 561 is formed by alternatively winding a long exciting coil
rod along the coil guide plate 562 in the axial direction of the heating
roller 566. In the exciting coil 561, an oscillation circuit is connected
to a driving source (not shown) which is variable in frequency. On the
outside of the exciting coil 561, an exciting coil core 563 that is
formed in a half cylinder shape and is of a ferromagnetic material such
as ferrite is located closely to the exciting coil 561 in a state where
it is fixed at an exciting coil core supporting member 564.

[0367]In the electromagnetic induction heating type fixing device 570
shown in FIG. 11, the exciting coil 561 of the electromagnetic induction
heating unit 560 is electrified, an alternating magnetic field is formed
around the electromagnetic induction heating unit 560, and the heating
roller 566 which is located closely to the exciting coil 561 and is
surrounded by the exciting coil 561 is uniformly and efficiently
pre-heated by excitation of overcurrent. A recording medium S with a
toner image T to be subjected to a fixing step formed thereon is conveyed
to a nip portion N between the fixing roller 580 and the pressurizing
roller 590. Then, the fixing belt 567 is heated by the heating roller 566
that has been heated at a predetermined temperature by effect of the
electromagnetic induction heating unit 560 in a contact portion W1 with
the heating roller 566, and the toner image T on the recording medium S
is heated to a molten state by the heated fixing belt 567. In this
condition, the recording medium S is inserted into a nip portion N formed
between the fixing roller 580 and the pressurizing roller 590. The
recording medium S inserted into the nip portion N is made contact with
the surface of the fixing belt 567 that is linked with rotation of the
fixing roller 580 and the pressurizing roller 590 to rotate and is
pressed at the time of passing through the nip portion N, thereby a toner
image T is fixed on the recording medium S.

[0368]Next, the recording medium S with the toner image T fixed thereon
passes through between the fixing roller 580 and the pressurizing roller
590 and is peeled off from the fixing belt 567 to be conveyed to a tray
(not shown). At that time, the recording medium S is ejected toward the
pressurizing roller 590 to prevent the recording medium S from being
wound around the fixing belt 567. The fixing belt 567 is cleaned by a
cleaning roller (not shown).

[0369]Further, an electromagnetic induction roller type fixing unit 525 as
shown in FIG. 12 is a fixing unit equipped with a fixing roller 520
serving as the fixing member, a pressurizing roller 530 that is located
so as to contact with the fixing roller 530, and electromagnetic
induction heating sources 540 that respectively heat the fixing roller
520 and the pressurizing roller 530 from the outside of the fixing roller
520 and the pressurizing roller 530.

[0370]The fixing roller 520 has a cored bar 521, and the surface of the
cored bar 521 is covered with a heat resistance elastic layer 522, a heat
generating layer 523 and a releasing layer 524 being formed in this
order. A pressurizing roller 530 has a cored bar 531, and the surface of
the cored bar 531 is covered with a heat resistance elastic layer 532, a
heat generating layer 533 and a releasing layer 534 being formed in this
order. The releasing layer 524 and the releasing layer 534 are formed of
tetrafluoroethylene-perfluoroalkyl vinyl ether (PFA).

[0371]The fixing roller 520 and the pressurizing roller 530 are biased by
a spring (not shown) and are rotatable formed in a pressure contact state
to form a nip portion N.

[0372]The electromagnetic induction heating sources 540 are respectively
located near the fixing roller 520 and the pressurizing roller 530 and
respectively heat the heat generating layer 523 and the heat generating
layer 533 by electromagnetic induction.

[0373]In the fixing device shown in FIG. 12, the fixing roller 520 and the
pressurizing roller 530 are uniformly and efficiently pre-heated by the
electromagnetic induction heating source 540. Because the fixing roller
520 and the pressurizing roller 530 are a combination of a roller and
another roller, they can easily make the nip portion N have a
high-surface pressure.

<Cleaning Step and Cleaning Unit>

[0374]The cleaning step is a step in which a residual toner remaining on
the surface of the latent electrostatic image bearing member is removed,
and the cleaning is preferably carried out by a cleaning unit.

[0375]The cleaning the surface of the latent electrostatic image bearing
member can be carried out without providing with a leaning unit by
providing a developing unit having a developer carrier that makes contact
with the latent electrostatic image bearing member and being configured
to develop a latent electrostatic image formed on the latent
electrostatic image bearing member and to collect a residual toner
remaining on the surface of the latent electrostatic image bearing member
(cleaning-less method).

[0376]The cleaning unit is not particularly limited as long as a residual
electrophotographic toner remaining on the electrophotographic
photoconductor can be removed by means of the cleaning unit. The cleaner
may be suitably selected from among those known in the art. Preferred
examples thereof include magnetic brush cleaners, electrostatic brush
cleaners, magnetic roller cleaners, blade cleaners, brush cleaners and
web cleaners. Of these cleaning units, cleaning blades are particularly
preferable in terms of their high-toner removability, compactness and
low-cost.

[0377]For a material of a rubber blade used for the cleaning blade, for
example, urethane rubbers, silicone rubbers, fluorine rubbers,
chloroprene rubbers and butadiene rubbers are exemplified. Of these,
urethane rubbers are particularly preferable.

[0378]Here, FIG. 13 is an enlarged illustration of the proximity of a
contact portion 615 between a cleaning blade 613 and a latent
electrostatic image bearing member 1 (may be referred to as
photoconductor drum 1). The cleaning blade 613 is formed with a toner
inhibiting surface 617 which forms, between the cleaning blade 613 and a
photoconductor drum 1, a space S that opens from the contact portion 615
toward the upstream of the rotational direction of the photoconductor
drum 1, with the surface of the photoconductor drum 1. In this
embodiment, the toner inhibiting surface 617 is set so that the space S
is formed to have an acute angle from the contact portion 615 to the
upstream of the rotational direction of the photoconductor drum 1.

[0379]On the toner inhibiting surface 617, as shown in FIG. 13, a coating
part 618 is provided as a portion having a high friction coefficient that
is highly frictioned by the cleaning blade 613. The coating part 618 is
formed with a material having a friction coefficient higher than that of
a material used for the cleaning blade 613. Examples of the material
having a high-friction coefficient include DLCs (diamond-like carbons).
The material having a high-friction coefficient is not particularly
limited to DLCs (diamond-like carbons). The coating part 618 is formed in
the toner inhibiting surface 617 such that it does not contact with the
surface of the photoconductor drum 1.

[0380]Note that the cleaning unit is not illustrated in the figure,
however, is provided with a toner collecting blade that collects a
residual toner scraped by the cleaning blade 613 and a toner collecting
coil that transports the residual toner collected by the toner collecting
blade to a collection site and may be further provided with other
members.

--Image Forming Apparatus Based on Cleaning-Less Method--

[0381]FIG. 14 is a schematic view showing one example of an image forming
apparatus based on cleaning-less method in which a developing unit also
serves as a cleaning unit.

[0383]In the cleaning-less image forming apparatus, a residual toner on
the photoconductor drum 1 is conveyed to a position of the contact type
brush charger 620 making contact with the photoconductor drum 1 by
successive rotation of the photoconductor drum 1, is temporarily
collected by a magnetic brush (not shown) of the brush charger 621 making
contact with the photoconductor drum 1. The collected toner is ejected to
the surface of the photoconductor drum 1 again, is ultimately collected
by a developer carrier 631 together with the developer into the
developing device 604, and is repeatedly used on the photoconductor drum
1 for image formation.

[0384]Here, "the developing unit 604 also serves as a cleaning unit" means
that a small amount of a residual toner on the photoconductor drum 1
after transfer is collected by effect of a developing bias (an electric
potential difference between a direct current voltage applied to the
developer carrier 631 and the surface electric potential of the
photoconductor drum 1).

[0385]In such a cleaning-less image forming apparatus in which a
developing unit also serves as a cleaning unit, a transfer residual toner
is collected by the developing device 604 and is to be used in the
subsequent operation, and therefore, it is greatly advantageous in
space-saving because it saves a waste toner, achieves maintenance-free
and cleaner-less system and allows for making an image forming apparatus
drastically compact.

<Other Steps and Other Units>

[0386]The charge eliminating step is a step in which a charge elimination
bias is applied to the latent electrostatic image bearing member to
remove a charge, and the charging is preferably carrier out by a charge
eliminating unit.

[0387]The charge eliminating unit is not particularly limited, as long as
it can apply a charge elimination bias to the latent electrostatic image
bearing member, and may be suitably selected from among conventional
charge eliminating devices. Preferred examples thereof include charge
eliminating lamps.

[0388]The recycling step is a step in which the electrophotographic toner
removed in the cleaning step is recycled to the developing unit, and the
recycling is preferably carried out by a recycling unit. The recycling
unit is not particularly limited, and examples thereof include
conventional conveying units.

[0389]The controlling step is a step in which the above-noted respective
steps are controlled, and the controlling can be preferably carried out
by a controlling unit.

[0390]The controlling unit is not particularly limited as long as it can
control operations of the above-noted respective units, and may be
suitably selected in accordance with the intended use. Examples thereof
include equipment such as sequencers and computers.

--Image Forming Apparatus and Image Forming Method--

[0391]Hereinafter, an aspect in which the image forming method of the
present invention is carried out by an image forming apparatus according
to the present invention will be explained with reference to FIG. 15. An
image forming apparatus 100 shown in FIG. 15 is provided with a
photoconductor drum 10 (a latent electrostatic image bearing member 10)
as a latent electrostatic image bearing member, a charging roller 20 as a
charging unit, an exposure 30 by means of an exposing device as an
exposing unit, a developing device 40 as a developing unit, an
intermediate transfer member 50, a cleaning blade 60 as a cleaning unit
and a charge eliminating lamp 70 as a charge eliminating unit.

[0392]The intermediate transfer member 50 is an endless belt and is
designed to be movable in the direction indicated by the arrow by tree
rollers 51 that are located inside of the intermediate transfer member 50
and respectively span the intermediate transfer member 50. A part of the
tree rollers 51 functions as a transfer bias roller that can apply a
predetermined transfer bias (primary transfer bias) to the intermediate
transfer member 50. Near the intermediate transfer member 50, an
intermediate transfer member cleaning blade 90 is located, and a transfer
roller 80 serves as the transfer unit which can apply a transfer bias for
secondarily transferring a visual image (toner image) onto a recording
medium 95 is placed to face the intermediate transfer member 50. Around
the intermediate transfer member 50, a corona charger 58 for applying a
charge to the visual image on the intermediate transfer member 50 is
located in between a contact position between the latent electrostatic
image bearing member 10 and the intermediate transfer member 50 and a
contact position between the intermediate transfer member 50 and the
recording medium 95.

[0393]The developing device 40 is composed of a developing belt 41 as a
developer carrier, a black developing unit 45K, a yellow developing unit
45Y, a magenta developing unit 45M and a cyan developing unit 45C which
are arranged around the developing belt 41. The black developing unit 45K
is equipped with a developer container 42K, a developer supplying roller
43K and a developing roller 44K. The yellow developing unit 45Y is
provided with a developer container 42Y, a developer supplying roller 43Y
and a developing roller 44Y. The magenta developing unit 45M is equipped
with a developer container 42M, a developer supplying roller 43M and a
developing roller 44M. The cyan developing unit 45C is equipped with a
developer container 42C, a developer supplying roller 43C and a
developing roller 44C. The developing belt 41 is an endless belt and is
rotatably spanned over a plurality of belt rollers, and a part thereof
makes contact with the latent electrostatic image bearing member 10.

[0394]In the image forming apparatus 100 shown in FIG. 15, first, the
charging roller 20 uniformly charges the photoconductor drum 10, the
exposing device (not shown) imagewisely exposes the surface of the
photoconductor drum 10 (exposure 30) to form a latent electrostatic
image. The latent electrostatic image formed on the photoconductor drum
10 is developed by supplying a toner from the developing device 40
thereto to form a visible image. The visible image is primarily
transferred onto the intermediate transfer member 50 by a voltage applied
from the rollers 51 (primary transfer) and further transferred onto the
recording medium 95 (secondary transfer). As a result, a transfer image
is formed on the recording medium 95. A residual toner remaining on the
surface of the latent electrostatic image bearing member 10 is removed by
the cleaning blade 60, and a charge remaining on the latent electrostatic
image bearing member 10 is once removed by the charge eliminating lamp
70.

[0395]Next, another aspect in which the image forming method of the
present invention is carried out by an image forming apparatus of the
present invention will be explained with reference to FIG. 16. An image
forming apparatus 100 shown in FIG. 16 is not equipped with the
developing belt 41 serving as a developer carrier as in the image forming
apparatus 100 shown in FIG. 15 and has the same structure and the same
operational effects as those of the image forming apparatus 100 shown in
FIG. 15, except that a black developing unit 45K, a yellow developing
unit 45Y, a magenta developing unit 45M and a cyan developing unit 45C
are directly arranged around a latent electrostatic image bearing member
10 so as to face the latent electrostatic image bearing member 10. The
same components as shown in FIG. 16 are denoted at the same numerals as
shown in FIG. 15.

--Tandem Type Image Forming Apparatus and Image Forming Method--

[0396]A still another aspect in which the image forming method of the
present invention is carried out by using an image forming apparatus
according to the present invention will be explained with reference to
FIG. 17. The tandem type image forming apparatus shown in FIG. 17 is a
tandem type color image forming apparatus. The tandem type color image
forming apparatus is equipped with a copier main body 150, a sheet feeder
table 200, a scanner 300 and an automatic document feeder 400.

[0397]The copier main body 150 includes an endless belt intermediate
transfer member 50 at its center part. The intermediate transfer member
50 is spanned over three support rollers 14, 15, and 16 and is capable of
rotating and moving in a clockwise direction in FIG. 17. An
intermediate-transfer-member cleaning unit 17 is capable of removing a
residual toner from the intermediate transfer member 50 after image
transfer and is placed near the support roller 15. Above the intermediate
transfer member 50 spanned between the support rollers of 14 and 15, a
tandem type developing unit 120 is placed so that yellow, cyan, magenta,
and black image forming units (image forming sections) 18, namely four
image forming units (four image forming sections), are arrayed in
parallel to face the intermediate transfer member 50 in the moving
direction of the intermediate transfer member 50. An exposer 21 is
arranged in the vicinity of the tandem type developing unit 120. A
secondary transfer unit 22 faces the tandem type developing unit 120 with
the interposition of the intermediate transfer member 50. The secondary
transfer unit 22 is equipped with an endless belt serving as secondary
transferring belt 24 which is spanned over a pair of rollers 23. A
recording medium being transported on the secondary transferring belt 24
can make contact with the intermediate transfer member 50. A fixing
device 25 is placed on the side of the secondary transfer unit 22.

[0398]A sheet reverser 28 is located in the vicinity of the secondary
transfer unit 22 and the fixing device 25. The sheet reverser 28 is
capable of reversing the recording medium so as to form images on both
sides of the recording medium.

[0399]Hereinafter, the way of forming a full-color image, i.e. the way a
color copy is formed by using the tandem type developing unit 120 will be
described. Initially, a document is placed on a document platen 130 of
the automatic document feeder (ADF) 400. Alternatively, the automatic
document feeder (ADF) 400 is opened, a document is placed on a contact
glass 32 of the scanner 300, and the automatic document feeder (ADF) 400
is closed to press the document.

[0400]When pushing a start switch (not shown), the document placed on the
automatic document feeder 400 is transported onto the contact glass 32.
When the document is initially place on the contact glass 32, the scanner
300 is immediately driven to operate a first carriage 33 and a second
carriage 34. Light is applied from a light source to the document by
action of the first carriage 33, and reflected secondary light from the
document is further reflected toward the second carriage 34. The
reflected light is further reflected by a mirror of the second carriage
34 and passes through an image-forming lens 35 into a read sensor 36 to
thereby read the color document, i.e. color image and to produce black,
yellow, magenta and cyan image information.

[0401]Each of the black, yellow, magenta, and cyan image information is
transmitted to each of the image forming units 18, i.e. black, yellow,
magenta, and cyan image forming units in the tandem type developing unit
120 to thereby form individual toner images in black, yellow, magenta and
cyan toner. Specifically, each of the image forming units 18 (black image
forming unit, yellow image forming unit, magenta image forming unit and
cyan image forming unit) in the tandem type developing unit 120 is
equipped with, as shown in FIG. 18, latent electrostatic image bearing
members 10 (black latent electrostatic image bearing member 10K, yellow
latent electrostatic image bearing member 10Y, magenta latent
electrostatic image bearing member 10M and cyan latent electrostatic
image bearing member 10C); a charger 60 configured to uniformly charge
the latent electrostatic image bearing member 10; an exposer configured
to expose the latent electrostatic image bearing member imagewisely
corresponding to each color image based on each color image information,
which is represented by L in FIG. 18, to form a latent electrostatic
image corresponding to each color images on the latent electrostatic
image bearing member; an image developing device 61 configured to develop
the latent electrostatic image using each color toner, i.e. black toner,
yellow toner, magenta toner, and cyan toner to form a toner image which
contains each of these color toners; a transfer charger 62 for
transferring the toner image onto the intermediate transfer member 50; a
cleaning device 63 and a charge-eliminator 64 to thereby respectively
form a monochrome image, i.e. a black image, a yellow image, a magenta
image and a cyan image based on the respective color image information.
The thus formed black image, yellow image, magenta image and cyan image,
i.e. the black image formed on the black latent electrostatic image
bearing member 10K, the yellow image formed on the yellow latent
electrostatic image bearing member 10Y, the magenta image formed on the
magenta latent electrostatic image bearing member 10M, and the cyan image
formed on the cyan latent electrostatic image bearing member 10C are
sequentially transferred (primary transfer) onto the intermediate
transfer member 50 which is rotated and shifted by the support rollers
14, 15, and 16. Then, the black image, the yellow image, the magenta
image and the cyan image are superimposed on the intermediate transfer
member 50 to thereby form a composite color image, i.e. a transferred
color image.

[0402]In the meanwhile, one of feeder rollers 142 in the feeder table 200
is selectively rotated, sheets or recording media are ejected from one of
multiple feeder cassettes 144 in a paper bank 143 and are separated by a
separation roller 145 one by one into a feeder path 146, and are
transported by transport roller 147 into feeder path 148 in the copier
main body 150 and are bumped against a resist roller 49 and stopped.
Alternatively, a feeder roller 142 is rotated to eject sheets or
recording media on a manual bypass tray 54, the sheets are separated one
by one by the separation roller 145 into a manual bypass feeder path 53
and are bumped against the resist roller 49 and stopped. The resist
roller 49 is generally grounded, however, may be used under the
application of a bias to remove paper dust of sheets.

[0403]The resist roller 49 is rotated in synchronization with the movement
of the composite color image, i.e. transferred color image on the
intermediate transfer member 50 to transport the recording medium into
between the intermediate transfer member 50 and the secondary transfer
unit 22, and the composite color image, i.e. transferred color image is
transferred onto the recording medium by action of the secondary transfer
unit 22 (secondary transfer) to thereby transfer the color image to the
recording medium. Separately, the intermediate transfer member cleaning
device 17 removes a residual toner remaining on the intermediate transfer
member 50 after image transfer.

[0404]The recording medium bearing the transferred color image is
transported by the secondary transfer unit 22 into the fixing device 25,
is applied with heat and pressure in the fixing device 25 to fix the
composite color image, i.e. transferred color image on the recording
medium. The recording medium then changes its direction by action of a
switch blade 55 and ejected by an ejecting roller 56 to be stacked on an
output tray 57. Alternatively, the recording medium changes its direction
by action of the switch blade 55 into the sheet reverser 28, turns
therein, is transported again to the transfer position, followed by image
formation on the backside of the sheet. The recording medium bearing
images on both sides thereof is ejected through the ejecting roller 56
and then stacked onto the output tray 57.

(Toner Container)

[0405]The toner container according to the present invention houses the
toner or the developer of the present invention.

[0406]The container is not particularly limited and may be suitably
selected from among conventional toner containers. For example, a toner
container having a toner container main body and a cap is preferably
exemplified.

[0407]The toner container is not particularly limited as to the size,
shape, structure, material and the like and may be suitably selected in
accordance with the intended use. For example, as to the shape, a
cylindrical shape is preferable. As to the structure, a container is
particularly preferable in which a continuous spiral convexoconcave is
formed on the inner surface, a toner contained in the container can be
moved toward the outlet by rotating the toner container and a part of the
spiral portion or the whole thereof has an accordion function.

[0408]Material of the toner container main body is not particularly
limited. A material that is formable with excellent dimensional precision
is preferable. Preferred examples thereof include resins. Among resins,
for example, polyester resins, polyethylene resins, polypropylene resins,
polystyrene resins, polyvinyl chloride resins, polyacrylic resins,
polycarbonate resins, ABS resins, polyacetal resins and the like are
preferably exemplified.

[0409]The toner container allows for easy storage and easy transportation,
is excellent in handleability, detachably mounted to the process
cartridge and the image forming apparatus of the present invention and
can be preferably used for toner supplement.

(Process Cartridge)

[0410]The process cartridge of the present invention has at least a latent
electrostatic image bearing member that carries a latent electrostatic
image thereon and a developing unit configured to develop the latent
electrostatic image carried on the latent electrostatic image bearing
member using a toner to form a visible image and further has other units
suitably selected in accordance with necessity such as a charging unit,
an exposing unit, a transfer unit, a cleaning unit and a charge
eliminating unit.

[0411]For the toner, the toner of the present invention is used.

[0412]The developing unit has at least a developer container that houses
the toner or the developer therein and a developer carrier that carries
and transports the toner or the developer housed in the developer
container and may further have a layer thickness controlling member for
controlling a toner layer thickness to be carried on the developer
carrier. Specifically, any one of the one-component developing unit and
the two-component developing unit which have been explained in the
sections of the image forming apparatus and the image forming method can
be suitably used.

[0413]Further, for the charging unit, exposing unit, transfer unit,
cleaning unit and charge eliminating unit, it is possible to selected
from those similarly to the respective units explained above in the
section of the image forming apparatus and to use them.

[0414]The process cartridge can be detachably mounted to various
electrophotographic image forming apparatuses, electrophotographic
facsimiles and electrophotographic printers, and it is particularly
preferable that the process cartridge be detachably mounted to the image
forming apparatus of the present invention.

[0415]The process cartridge incorporates, as shown in FIG. 19, a latent
electrostatic image bearing member 101, a charging unit 102, a developing
unit 104, a transfer unit 108 and a cleaning unit 107 and further has
other units in accordance with necessity. In FIG. 19, a reference numeral
103 denotes exposure using an exposing unit, and a reference numeral 105
denotes a recording medium.

[0416]Next, in an image forming process using the process cartridge shown
in FIG. 19, the latent electrostatic image bearing member 101 goes
through charging by the charging unit 102 and exposure 103 by the
exposing unit (not shown) while rotating in the direction indicated by
the curved arrow, and a latent electrostatic image corresponding to an
exposed image is formed of the surface of the latent electrostatic image
bearing member 101. The latent electrostatic image is developed by the
developing unit 104 to form a visual image, and the obtained visual image
is transferred onto the recording medium 105 by the transfer unit 108 to
be printed out. Subsequently, the surface of the latent electrostatic
image bearing member after the image transfer is cleaned by the cleaning
unit 107, and further, a residual charge remaining thereon is eliminated
by a charge eliminating unit. The operations stated above are repeated
again.

[0417]Because the toner of the present invention is used in the image
forming apparatus, the image forming method and the process cartridge of
the present invention, the image forming apparatus, the image forming
method and the process cartridge respectively allow for forming extremely
high-quality images for a long period of time without causing a change in
color tone and abnormal images such as a reduction in image density and
background smear.

EXAMPLES

[0418]Hereinafter, the present invention will be further described in
detail referring to specific Examples, however, the present invention is
not limited to the disclosed Examples.

[0419]In the following Examples and Comparative Examples, "softening point
of resin", "softening point of rosin", "glass transition temperature (Tg)
of resin and rosin" and "acidic value of resin and rosin" were
respectively measured as follows.

<Measurement of Softening Point of Resin>

[0420]Using a flow tester (CFT-500D, manufactured by Shimadzu
Corporation), 1 gram of resin was heated as a sample at a temperature
increasing rate of 6° C./min under application of a load of 1.96
MPa using a plunger. The resin sample was extruded from a nozzle of 1 mm
in diameter and 1 mm in length, the descent amounts of the plunger of the
flow tester to temperatures were plotted, and the temperature at the
point in time when the half value of the resin sample flowed out was
determined as the softening point of the resin.

<Measurement of Softening Point of Rosin>

(1) Preparation of Sample

[0421]Ten grams of rosin was dissolved on a hot plate for 2 hours at a
temperature of 170° C. Thereafter, the rosin was naturally cooled
down for 1 hour with the lid off under an environmental condition of
25° C. and a relative humidity of 50% and then crushed in a coffee
mill (MK-61M, manufactured by Matsushita Electric Industrial Co., Ltd.)
for 10 seconds to prepare a sample.

(2) Measurement

[0422]Using a flow tester (CFT-500D, manufactured by Shimadzu
Corporation), 1 gram of rosin was heated as a sample at a temperature
increasing rate of 6° C./min under application of a load of 1.96
MPa using a plunger. The rosin sample was extruded from a nozzle of 1 mm
in diameter and 1 mm in length, the descent amounts of the plunger of the
flow tester to temperatures were plotted, and the temperature at the
point in time when the half value of the rosin sample flowed out was
determined as the softening point of the rosin.

<Measurement of Glass Transition Temperature (Tg) of Resin/Rosin>

[0423]A measurement sample was weighed 0.01 g to 0.02 g in an aluminum
pan. Using a differential scanning calorimetry (DSC210, manufactured by
Seiko Electronics Industries Co., Ltd.), the temperature of the sample
was increased to 200° C. and then decreased to 0° C. from
200° C. at a temperature decreasing rate of 10° C./min, the
temperature of the cooled sample was again increased at a temperature
increasing rate of 10° C./min, and the intersection point between
an extended line of a base line drawn with the maximum endothermic peak
temperature or lower than the maximum endothermic peak temperature and a
tangent line showing an maximum angle of inclination from an initial rise
point (rising edge) of the endothermic peak temperature to the maximum
endothermic peak temperature was determined as the glass transition
temperature of the sample.

<Acidic Value of Resin/Rosin>

[0424]The acidic value of resin and rosin was measured based on the method
described in JIS K0070. However, only a mixed solvent of acetone and
toluene (acetone:toluene=1:1 (volume ratio)) was used for measurement
instead of the mixed solvent of ethanol and ether specified in JIS K0070.

Synthesis Example 1

Purification of Rosin

[0425]Into a 2,000-mL distillation flask of equipped with a fractionating
column, a reflux condenser and a receiver, 1,000 g of a tall rosin was
added, the content of the flask was distilled under a reduced pressure of
1 kPa, and a distillate collected at a temperature of 195° C. to
250 as the main distillate. Hereinafter, the tall rosin used in
purification will be referred to as an unpurified rosin, and the rosin
collected as the main distillate will be referred to as a purified rosin.

[0426]In a coffee mill (MK-61M, manufactured by Matsushita Electric
Industrial Co., Ltd.), 20g of each rosin was crushed for 5 seconds, and
the crushed rosin was filtered through a mesh with a pore diameter of 1
mm, and the filtrate was weighed 0.5 g and poured in a head space vial
(20 mL). The head space gas was sampled, and impurities in the unpurified
rosin and impurities in the purified rosin were analyzed by head space
DC-MS method in the following manner. Table 1 shows the analysis results.

[0450]The alcohol components, terephthalic acid and esterification
catalyst shown in the column of Resin H1 in Table 2 were poured into a
5-litter four-necked flask equipped with a nitrogen inlet tube, a
dewatering tube, a stirrer and a thermocouple sensor, the components in
the flask were subjected to a condensation polymerization reaction in
nitrogen atmosphere at 230° C. for 15 hours and then reacted at
230° C. under a pressure of 8.0 kPa for 1 hour. The reactant was
cooled down to 180° C., then the purified rosin was poured in the
flask, and the components were further reacted at 200° C. for 15
hours. The reactant was cooled down to 180° C. again, then
itaconic acid was poured in the flask, and the components were further
reacted at 200° C. for 8 hours. The resulting product was cooled
down to 180° C., then trimellitic anhydride was poured in the
flask, and the temperature of the content of the flask was increased to
210° C. for 2 hours and reacted at 210° C. under a pressure
of 10 kPa until a desired softening point to thereby synthesize a
polyester resin (Resin H1).

Synthesis Example 3

Synthesis of Polyester Resin

[0451]The alcohol component, terephthalic acid and esterification catalyst
shown in the column of Resin L1 in Table 3 were poured into a 5-litter
four-necked flask equipped with a nitrogen inlet tube, a dewatering tube,
a stirrer and a thermocouple sensor, the components in the flask were
subjected to a condensation polymerization reaction in nitrogen
atmosphere at 230° C. for 15 hours and then reacted at 230°
C. under a pressure of 8.0 kPa for 1 hour. The reactant was cooled down
to 180° C., then the purified rosin was poured in the flask, and
the components were further reacted at 200° C. for 15 hours. The
reactant was cooled down to 180° C. again, then itaconic acid was
poured in the flask, and the temperature of the content of the flask was
increased to 210° C. for 2 hours and the content was reacted at
210° C. under a pressure of 10 kPa until a desired softening point
to thereby synthesize a polyester resin (Resin L1).

Synthesis Example 4

Synthesis of Polyester Resin

[0452]The alcohol component, terephthalic acid and esterification catalyst
shown in the column of Resin L2 in Table 3 were poured into a 5-litter
four-necked flask equipped with a nitrogen inlet tube, a dewatering tube,
a stirrer and a thermocouple sensor, the components in the flask were
subjected to a condensation polymerization reaction in nitrogen
atmosphere at 230° C. for 15 hours and then reacted at 230°
C. under a pressure of 8.0 kPa for 1 hour. The reactant was cooled down
to 180° C., then itaconic acid was poured in the flask, and the
temperature of the content of the flask was increased to 210° C.
for 2 hours and the content was reacted at 210° C. under a
pressure of 10 kPa until a desired softening point to thereby synthesize
a polyester resin (Resin L2).

Synthesis Example 5

Synthesis of Polyester Resin

[0453]The alcohol components, terephthalic acid and esterification
catalyst shown in the columns of Resin H2, Resin H3, Resin H4 and Resin
H8 in Table 2 were respectively poured into a 5-litter four-necked flask
equipped with a nitrogen inlet tube, a dewatering tube, a rectification
column, a stirrer and a thermocouple sensor, the components in the flask
were subjected to a condensation polymerization reaction in nitrogen
atmosphere at 230° C. for 15 hours and then reacted at 230°
C. under a pressure of 8.0 kPa for 1 hour. The reactant was cooled down
to 180° C., then trimellitic anhydride was poured in the flask,
and the temperature of the content of the flask was increased to
210° C. for 3 hours, the content was reacted under normal pressure
of 101.3 kPa for 10 hours and then reacted at 210° C. under a
pressure of 20 kPa until a desired softening point to thereby synthesize
polyester resins (Resin H2, Resin H3, Resin H4 and Resin H8),
respectively.

Synthesis Example 6

Synthesis of Polyester Resin

[0454]The alcohol components, terephthalic acid and esterification
catalyst shown in the columns of Resin H5, Resin H6, Resin L3, Resin L4
and Resin L5 in Table 2 were respectively poured into a 5-litter
four-necked flask equipped with a nitrogen inlet tube, a dewatering tube,
a rectification column, a stirrer and a thermocouple sensor, the
components in the flask were subjected to a condensation polymerization
reaction in nitrogen atmosphere at 230° C. for 15 hours and then
reacted at 230° C. under a pressure of 20 kPa until a desired
softening point to thereby synthesize polyester resins (Resin H5, Resin
H6, Resin L3, Resin L4 and Resin L5), respectively.

Synthesis Example 7

Synthesis of Polyester Resin

[0455]Into a 5 litter four-necked flask equipped with a nitrogen inlet
tube, a dewatering tube, a rectification column, a stirrer and a
thermocouple sensor, 6 mol of bisphenol A propylene oxide, 4 mol of
bisphenol A ethylene oxide, 8 mol of terephthalic acid and 3 mol of
trimellitic anhydride were poured, the components were subjected to a
condensation polymerization reaction in nitrogen atmosphere at
220° C. for 15 hours and then reacted at 220° C. under a
pressure of 20 kPa until a desired softening point to thereby synthesize
a polyester resin (Resin L6).

[0456]The obtained Resin L6 had a softening point of 106.3° C., a
glass transition temperature of 59.0° C. and an acidic value of
21.0 mgKOH/g.

Synthesis Example 8

Synthesis of Polyester Resin

[0457]Into a 5-litter four-necked flask equipped with a nitrogen inlet
tube, a dewatering tube, a rectification column, a stirrer and a
thermocouple sensor, 6 mol of bisphenol A propylene oxide, 4 mol of
bisphenol A ethylene oxide, 10 mol of fumaric acid and 4 mol of
trimellitic anhydride were poured, the components were subjected to a
condensation polymerization reaction in nitrogen atmosphere at
220° C. for 15 hours and then reacted at 220° C. under a
pressure of 20 kPa until a desired softening point to thereby synthesize
a polyester resin (Resin H7).

[0458]The obtained Resin H7 had a softening point of 142.5° C., a
glass transition temperature of 63.1° C. and an acidic value of
28.1 mgKOH/g.

[0459]In a vessel, 3 mol of 3,5-di-t-butyl salicylate and caustic soda
were dissolved in water, and 1.5 mol of ferric chloride (FeCL3)
aqueous solution was delivered by drops thereinto while stirring the
dissolved solution at 60° C. to obtain a crystal. The crystal was
filtered, washed, dried and pulverized to thereby synthesize a dusky
black powder (Aromatic Oxycarboxylic Acid Metal Compound 1). The
following is the structural formula of the obtained Aromatic
Oxycarboxylic Acid Metal Compound 1.

[0461]In a vessel, 4 mol of 3,5-di-t-butyl salicylate and caustic soda
were dissolved in water, and 1 mol of zirconium chloride (ZrCl2)
aqueous solution was delivered by drops thereinto while stirring the
dissolved solution at 50° C. to obtain a crystal. The crystal was
filtered, washed, dried and pulverized to thereby synthesize a white
powder (Aromatic Oxycarboxylic Acid Metal Compound 2). The following is
the structural formula of the obtained Aromatic Oxycarboxylic Acid Metal
Compound 2.

[0463]In a vessel, 5 mol of 3,5-di-t-butyl salicylate and caustic soda
were dissolved in water, and 4 mol of zirconium oxychloride
(ZrOCl2.8H2O) aqueous solution was delivered by drops thereinto
while stirring the dissolved solution at 50° C. to obtain a
crystal. The crystal was filtered, washed, dried and pulverized to
thereby synthesize a white powder (Aromatic Oxycarboxylic Acid Metal
Compound 3). The following is the structural formula of the obtained
Aromatic Oxycarboxylic Acid Metal Compound 3.

[0465]A pigment having the following composition, Resin L1 and pure water
were mixed at a mixing ratio of 1:1:0.5 (mass ratio) and the mixture was
kneaded with two rollers at a temperature of 70° C. Then, the
temperature of the two rollers was increased to 120° C. to
evaporate water to thereby prepare Masterbatch 1 composed of Cyan Toner
Masterbatch 1 (MB-C1), Magenta Toner Masterbatch 1 (MB-M1), Yellow Toner
Masterbatch 1 (MB-Y1) and Black Toner Masterbatch 1 (MB-K1).

[0472]A Cyan Toner Formulation 1 having the following composition was
preliminarily mixed using a HENSCHEL MIXER (FM10B, manufactured by Mitsui
Miike Kakoki K.K.) and then was melt-kneaded at a temperature of
100° C. to 130° C. using a biaxial kneader (PCM-30,
manufactured by IKEGAI LTD.). The obtained kneaded product was cooled
down to room temperature and then coarsely crushed using a hammer mill so
as to have particle diameters of 200 μm to 400 μm. Subsequently,
the coarsely crushed product was pulverized using a ultrasonic jet
pulverizer (LABO-JET, manufactured by Nippon Pneumatic Manufacturing Co.,
Ltd.) and the pulverized product was classified using an airflow
classifier (MDS-I, manufactured by Nippon Pneumatic Manufacturing Co.,
Ltd.) to thereby prepare a toner base particle.

[0473]Next, 1.0 part by mass of an additive (HDK-2000, manufactured by
Clariant Japan K.K.) was added to 100 parts by mass of the toner base
particle in a HENSCHEL MIXER, then stirred and mixed therein, thereby
preparing Cyan Toner 1.

[0474]Magenta Toner 1 was prepared in the same manner as in the Cyan Toner
1 production method except that the Cyan Toner Formulation 1 was changed
to a Magenta Toner Formulation 1 having the following composition.

[0475]Yellow Toner 1 was prepared in the same manner as in the Cyan Toner
1 production method except that the Cyan Toner Formulation 1 was changed
to a Yellow Toner Formulation 1 having the following composition.

[0476]Black Toner 1 was prepared in the same manner as in the Cyan Toner 1
production method except that the Cyan Toner Formulation 1 was changed to
a Black Toner Formulation 1 having the following composition.

[0477]Toner 2 composed of Cyan Toner 2, Yellow Toner 2, Magenta Toner 2
and Black Toner 2 was prepared in the same manner as in Example 1 except
that the respective toner formulations were changed to the following
toner formulations.

[0478]Toner 3 composed of Cyan Toner 3, Yellow Toner 3, Magenta Toner 3
and Black Toner 3 was prepared in the same manner as in Example 1 except
that the respective toner formulations were changed to the following
toner formulations.

[0479]Toner 4 composed of Cyan Toner 4, Yellow Toner 4, Magenta Toner 4
and Black Toner 4 was prepared in the same manner as in Example 1 except
that the respective toner formulations were changed to the following
toner formulations.

[0480]Toner 5 composed of Cyan Toner 5, Yellow Toner 5, Magenta Toner 5
and Black Toner 5 was prepared in the same manner as in Example 1 except
that the respective toner formulations were changed to the following
toner formulations.

[0481]Toner 6 composed of Cyan Toner 6, Yellow Toner 6, Magenta Toner 6
and Black Toner 6 was prepared in the same manner as in Example 1 except
that the respective toner formulations were changed to the following
toner formulations.

[0482]Toner 7 composed of Cyan Toner 7, Yellow Toner 7, Magenta Toner 7
and Black Toner 7 was prepared in the same manner as in Example 1 except
that the respective toner formulations were changed to the following
toner formulations.

[0483]Toner 8 composed of Cyan Toner 8, Yellow Toner 8, Magenta Toner 8
and Black Toner 8 was prepared in the same manner as in Example 1 except
that the respective toner formulations were changed to the following
toner formulations.

[0484]Toner 9 composed of Cyan Toner 9, Yellow Toner 9, Magenta Toner 9
and Black Toner 9 was prepared in the same manner as in Example 1 except
that the respective toner formulations were changed to the following
toner formulations.

[0485]Toner 10 composed of Cyan Toner 10, Yellow Toner 10, Magenta Toner
10 and Black Toner 10 was prepared in the same manner as in Example 1
except that the respective toner formulations were changed to the
following toner formulations.

[0486]Toner 11 composed of Cyan Toner 11, Yellow Toner 11, Magenta Toner
11 and Black Toner 11 was prepared in the same manner as in Example 1
except that the respective toner formulations were changed to the
following toner formulations.

[0487]Toner 12 composed of Cyan Toner 12, Yellow Toner 12, Magenta Toner
12 and Black Toner 12 was prepared in the same manner as in Example 1
except that the respective toner formulations were changed to the
following toner formulations.

[0488]Toner 13 composed of Cyan Toner 13, Yellow Toner 13, Magenta Toner
13 and Black Toner 13 was prepared in the same manner as in Example 1
except that the respective toner formulations were changed to the
following toner formulations

[0489]Toner 14 composed of Cyan Toner 14, Yellow Toner 14, Magenta Toner
14 and Black Toner 14 was prepared in the same manner as in Example 1
except that the respective toner formulations were changed to the
following toner formulations.

[0490]Toner 15 composed of Cyan Toner 15, Yellow Toner 15, Magenta Toner
15 and Black Toner 15 was prepared in the same manner as in Example 1
except that the respective toner formulations were changed to the
following toner formulations.

[0491]Toner 16 composed of Cyan Toner 16, Yellow Toner 16, Magenta Toner
16 and Black Toner 16 was prepared in the same manner as in Example 1
except that the respective toner formulations were changed to the
following toner formulations.

[0492]Next, the weight average particle diameter (D4) of the obtained
Toner 1 to Toner 16 prepared in Examples 1 to 8 and Comparative Examples
1 to 8 was measured as follows. Further, a difference in softening point
(ΔTm) between the used polyester resin (A) and the used polyester
resin (B), i.e., a difference between Tm (A) and Tm (B), was determined.
Tables 5-A, 5-B, 6-A and 6-B show the measurement results.

<Weight Average Particle Diameter of Toner>

[0493]The weight average particle diameter (D4) of each of the
prepared toners was measured by using a particle sizer (MULTISIZER III,
manufactured by Beckman Coulter Co.) with an aperture diameter of 100
μm, and each of the toners was analyzed using analysis software
(Beckman COULTER MULTISIZER 3 Version 3.51). Specifically, to a 100-mL
glass beaker, 0.5 mL of a 10% by mass surfactant (alkylbenzene sulfonate,
NEOGEN SC-A, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) was added,
the each of the obtained toners was added thereto, and the components
were stirred with a microspatula. Next, 80 mL of ion exchange water was
added thereto. The obtained dispersion liquid was dispersed using a
ultrasonic dispersing device (W-113MK-II, manufactured by HONDA
ELECTRONICS CO., LTD.) for 10 minutes. The weight average particle
diameter of the dispersion liquid was determined using the MULTISIZER
III. As a measurement solution, ISOTON III manufactured by Beckman
Coulter Co. was used. In the measurement, the toner sample dispersion
liquid was delivered by drops so that the concentration indicated by a
measuring device was 8% by mass±2% by mass. It is important that the
concentration of the toner sample dispersion liquid is set to 8% by
mass±2% by mass from the perspective of measurement repeatability of
particle diameter. When the concentration is within the range, the weight
average particle diameter of the sample can be measured causing no
measurement error.

[0494]For channels, the following 13 channels were used, and particles
having a particle diameter of 2.00 μm to less than 40.30 μm were
intended to be measured. A channel of 2.00 μm to less than 2.52 μm;
a channel of 2.52 μm to less than 3.17 μm; a channel of 3.17 μm
to less than 4.00 μm; a channel of 4.00 μm to less than 5.04 μm;
a channel of 5.04 μm to less than 6.35 μm; a channel of 6.35 μm
to less than 8.00 μm; a channel of 8.00 μm to less than 10.08
μm; a channel of 10.08 μm to less than 12.70 μm; a channel of
12.70 μm to less than 16.00 μm; a channel of 16.00 μm to less
than 20.20 μm; a channel of 20.20 μm to less than 25.40 μm; a
channel of 25.40 μm to less than 32.00 μm and a channel of 32.00
μm to less than 40.30 μm.

[0495]The weight of each of the toner samples was measured and the weight
distribution was calculated. The weight average particle diameter
(D4) of the toner sample was determined from the obtained weight
distribution.

[0496]Carrier A to be used in a two-component developer was prepared as
follows.

[0497]A coating material having the following composition was dispersed
using a stirrer for 10 minutes to prepare a coating solution. The coating
solution was poured to and 5,000 parts by mass of a core material (Mn
ferrite particle, mass average particle diameter=35 μm) was placed in
a coating device equipped with a rotatable bottom plate and stirring
blades in a fluidized bed while forming a swirling flow, thereby coating
the core material with the coating solution. The obtained coated material
was baked in an electric furnace at 250° C. for 2 hours to thereby
prepare Carrier A.

[0498]Next, with respect to the Toner 1 to Toner 16 obtained in Examples 1
to 8 and Comparative Examples 1 to 8, the pulverizability, heat
resistance/storage stability, charge rising property and chargeability at
the time of deterioration of toner were evaluated. Table 7 shows the
evaluation results.

--Measurement of Pulverizability--

[0499]Each of the melt-kneaded products shown in Tables 5-A, 5-B, 6-A and
6-B was coarsely crushed using a hammer mill so as to have particle
diameters of 200 μm to 400 μm. The crushed product was weighed
10.00 g, pulverized in a mill mixer (MM-I, manufactured by Hitachi Living
Systems Co.) for 30 seconds and filtered through a mesh of 30 in size
(pore diameter: 500 μm). Mass (g) (A) of the resin that did not get
through the mesh was weighed with accuracy, the residual ratio was
determined from the following Expression (i), and the process was
repeated three times. The results were averaged out, and the average
residual ratio was regarded as an indicator of pulverizability of the
toner. The pulverizability of the toner was evaluated based on the
following evaluation criteria. The lower the average value of the
residual ratio is, the more excellent in pulverizability the toner is.

[0505]The heat resistance/storage stability of the toner was measured
using a penetrator (manufactured by The Institute of Japanese Union of
Scientists and Engineers Co., Ltd.). Specifically, each of the toners was
weighed 10 g and placed in a 30-mL glass screw vial under the
environmental conditions of 20° C. to 25° C. and relative
humidity of 40% to 60%, and the lid of the vial was closed. The glass
vial with the toner contained therein was tapped against the desk top 100
times and then left intact in a thermostatic chamber with the temperature
set at 50° C. for 24 hours. Thereafter, the penetration of the
toner was measured using the penetrator, and the heat resistance/storage
stability of the toner was evaluated based on the following evaluation
criteria. The larger penetration value is, the more excellent in heat
resistance/storage stability the toner is.

[Evaluation Criteria]

[0506]A: The penetration value was 30 mm or more.

[0507]B: The penetration value was 20 mm to 29 mm.

[0508]C: The penetration value was 15 mm to 19 mm.

[0509]D: The penetration value was 8 mm to 14 mm.

[0510]E: The penetration value was 7 mm or less.

<Charge Rising Property>

[0511]In a 20-mL polyvinyl container, 0.6 g of each of the prepared toners
and 9.4 g of the prepared Carrier A were placed and then stirred for 30
seconds using a tubular mixer (T2F, manufactured by Willy A. Bachofen AG)
at 100 rpm to prepare a two-component developer. The charge amount
(μC/g) of the obtained two-component developer was determined using
"Q/M meter" (manufactured by Epping GmbH). The Q/M meter was set as
follows: a stainless-steel mesh (the mesh size: 400), soft-blow pressure:
1,050 V, and suction time: 90 seconds. The charge amount was determined
from the following Expression (ii). Under the above-noted conditions, the
higher the charge amount the more excellent in charge rising property the
toner is.

[0517]In a 20-mL polyvinyl container, 0.6 g of each of the prepared toners
and 9.4 g of the prepared Carrier A were placed and then stirred for 90
minutes using a tubular mixer (T2F, manufactured by Willy A. Bachofen AG)
at 100 rpm to prepare a two-component developer. The charge amount
determined at this point in time was regarded as Q90. The charge
amount (μC/g) of the obtained two-component developer was determined
using "Q/M meter" (manufactured by Epping GmbH). The Q/M meter was set as
follows: a stainless-steel mesh (the mesh size: 400), soft-blow pressure:
1,050 V, and suction time: 90 seconds. The charge amount was determined
from the above-noted Expression (ii). The charge amount of the
two-component developer was determined in the same manner as the
above-noted method except that the developer was stirred in the tabular
mixer at 100 rpm for 10 minutes. The charge amount determined at this
point in time was regarded as Q90. As an indicator of chargeability
at the time of deterioration of toner, a charge decrease rate at the time
of deterioration of toner was determined from the following Expression
(iii). The lower the charge decrease rate is, the higher charge stability
can be obtained to deterioration of toner.

[0523]An image forming apparatus (evaluation system A) shown in FIG. 20
was filled with each of the prepared toners to carry out image formation.
Various physical properties of each of the toners were evaluated as
follows. Table 8 shows the evaluation results.

[0525]The image forming apparatus (evaluation system A) shown in FIG. 20
uses a contact type charging roller as the charging unit 310 as shown in
FIG. 1 and uses a one-component developing device as the developing
device 324 as shown in FIG. 5. In the developing device, cleaner-less
process allowing for collecting a residual toner was employed. As the
fixing unit 327, a belt fixing device as shown in FIG. 9 was used, and
the fixing device uses a halogen lamp as heat source of the heating
roller. In FIG. 20, a reference numeral 330 denotes a conveyance belt.

[0526]In an image forming section 341 in the image forming apparatus
(evaluation system A) shown in FIG. 20, around a photoconductor drum 321,
a charging unit 310, an exposing unit 323, a developing unit 324 and a
transfer unit 325 are arranged. The photoconductor drum 321 in the image
forming section 341 goes through a charging step by the charging unit 310
and an exposing step by the exposing unit 323 while rotating to form a
latent electrostatic image corresponding to an exposed image on the
surface thereof. The latent electrostatic image is developed using a
yellow toner at the developing unit 324 to form a visible image of the
yellow toner on the photoconductor drum 321. The yellow toner visible
image is transferred onto a recording medium 326 by the transfer unit 325
and then a residual toner remaining on the photoconductor drum 321 is
collected by the developing unit 324. Similarly to the yellow toner, by
individual image forming sections 342, 343 and 344, visual images of
magenta toner, cyan toner and black toner are superimposed on the
recording medium 326, and a color image formed on the recording medium
326 is fixed by the fixing unit 327.

<Low-Temperature Fixing Property>

[0527]Using the evaluation system A, a solid image with an toner adhesion
amount of 0.85 mg/cm2±0.1 mg/cm2 was formed on a transfer
sheet of heavy paper (copy paper <135>, manufactured by NBS Ricoh
Co., Ltd.), and the image was fixed while changing the temperature of the
fixing belt. On the surface of the obtained fixed image, the image was
written using an image analysis equipment (AD-401, manufactured by
Ueshima Seisakusho Co., Ltd.) equipped with a ruby needle (tip radius:
260 μmR to 320 μmR, tip angle: 60 degrees) under a load of 50g. The
image surface was scrubbed strongly with a fiber (HANICOT #440,
manufactured by Haniron K.K. 5 times. The temperature of the fixing belt
at which there was little image exfoliation was determined as the fixing
lower limit temperature to thereby evaluate the low-temperature fixing
property based on the following criteria. The solid image was formed on
the transfer sheet at a position of 3.0 cm from the edge in the
paper-passing direction.

[Evaluation Criteria]

[0528]A: The fixing lower limit temperature was 125° C. or less.

[0529]B: The fixing lower limit temperature was 126° C. to
135° C.

[0530]C: The fixing lower limit temperature was 136° C. to
145° C.

[0531]D: The fixing lower limit temperature was 146° C. to
155° C.

[0532]E: The fixing lower limit temperature was 156° C. or more.

<Hot-Offset Resistance>

[0533]Using the evaluation system A, a solid image with an toner adhesion
amount of 0.85 mg/cm2±0.1 mg/cm2 was formed on a transfer
sheet of regular paper (Type 6200, manufactured by Ricoh Co., Ltd.), and
the image was fixed while changing the temperature of the fixing belt to
thereby perform a fixing test. Presence or absence of hot-offset was
visually checked. The upper limit temperature at which no hot-offset
occurred was determined as the fixing upper limit temperature, and the
hot-offset resistance was evaluated based on the following criteria. The
solid image was formed on the transfer sheet at a position of 3.0 cm from
the edge in the paper-passing direction.

[Evaluation Criteria]

[0534]A: The fixing upper limit temperature was 230° C. or more.

[0535]B: The fixing upper limit temperature was 210° C. to less
than 230°.

[0536]C: The fixing upper limit temperature was 190° C. to less
than 210°.

[0537]D: The fixing upper limit temperature was 180° C. to less
than 190°.

[0538]E: The fixing upper limit temperature was less than 180° C.

<Initial Image>

[0539]The image quality of the toner in the initial stage was evaluated as
follows. An image evaluation chart was output in full-color mode, and a
change in color tone, background smear, image density and presence or
absence of thinned image were evaluated. Presence or absence of abnormal
image and the image quality were visually checked and ranked in the
following five levels.

[Evaluation Criteria]

[0540]A: No abnormal image was observed, and the toner was excellent.

[0541]B: A slight difference in color tone (color tint), a slight change
in image density and background smear were observed as compared to the
original image, however, the toner was excellent and there would be no
problem in practical use.

[0542]C: A slight change in color tone (color tint), a slight change in
image density and background smear were observed.

[0543]D: A change in color tone (color tint), a change in image density
and background smear were clearly observed, and there would cause
problems in practical use.

[0544]E: A change in color tone (color tint), a change in image density
and background smear were severe, and it was impossible to obtain a
normal image.

<Temporal Stability>

[0545]After outputting an image chart with an image area of 80% (image
area in each color: 20%) in full-color mode using the evaluation system
A, the output image was evaluated in the same manner as in the evaluation
of initial image and compared to the initial image, to thereby evaluate
the temporal stability based on the following criteria.

[Evaluation Criteria]

[0546]A: No abnormal image was observed, and the toner was excellent.

[0547]B: As compared to the initial image, a slight difference in color
tone (color tint), a slight change in image density and background smear
were observed, however, the toner was on the level where there would be
no problem under normal temperature and humidity environments.

[0548]C: As compared to the initial image, a slight change in color tone
(color tint), a slight change in image density and background smear were
observed.

[0549]D: As compared to the initial image, a change in color tone (color
tint), a change in image density and background smear were clearly
observed, and there would cause problems in practical use.

[0550]E: As compared to the initial image, a change in color tone (color
tint), a change in image density and background smear were severe, and it
was impossible to obtain a normal image.

Example 17

[0551]A two-component developer was prepared using Toner 8 in the
following manner, and various physical properties of the toner were
evaluated in the same manner as in Example 16 an image forming apparatus
(evaluation system B) as shown in FIG. 21 explained below was used
instead of the evaluation system A. Table 8 shows the evaluation results.

--Preparation of Two-Component Developer--

[0552]For a carrier used in the tow-component developer, the prepared
carrier A stated above (ferrite carrier having an average particle
diameter of 35 μm, which was coated with a silicone resin of 0.5 μm
in average thickness) was used. Seven parts by mass of the each of the
toners was used to 100 parts by mass of the carrier, and the toner and
the carrier were placed in a tubular mixer (manufactured by Willy A.
Bachofen AG) in which the vessel tumbled over for stirring the content
therein to thereby uniformly mix the toner and the carrier at 48 rpm for
3 minutes and charge the two-component developer. In Example 17, 200g of
the carrier A and 14g of each of the toner were placed in a 500-mL
ointment bottle and mixed.

--Image Formation and Evaluation--

[0553]An image forming apparatus (evaluation system B) shown in FIG. 21
was filled with the thus prepared two-component developer to carry out
image formation. Various physical properties of each of the toners were
evaluated in the same manner as evaluated with the evaluation system A.
Table 8 shows the evaluation criteria.

[0555]The image forming apparatus (evaluation system B) shown in FIG. 21
uses a non-contact corona charger as the charging unit 311 as shown in
FIG. 3 and uses a two-component developing device as the developing
device 324 as shown in FIG. 6. As the cleaning unit 330, a cleaning blade
as shown in FIG. 10 is used. As the fixing unit 327, a roller fixing
device of electromagnetic induction heating type as shown in FIG. 12 was
used.

[0556]In an image forming section 351 in the image forming apparatus
(evaluation system B) shown in FIG. 21, around a photoconductor drum 321,
a charging unit 311, an exposing unit 323, a developing unit 324, a
primary transfer unit 325 and a cleaning unit 330 are arranged. The
photoconductor drum 321 in the image forming section 351 goes through a
charging step by the charging unit 310 and an exposing step by the
exposing unit 323 while rotating to form a latent electrostatic image
corresponding to an exposed image on the surface thereof. The latent
electrostatic image is developed using a yellow toner at the developing
unit 324 to form a visible image of the yellow toner on the
photoconductor drum 321. The yellow toner visible image is transferred to
an intermediate transfer belt 355 by the primary transfer unit 325, and a
residual yellow toner remaining on the photoconductor drum 321 is removed
by the cleaning unit 330. Similarly to the yellow toner, by individual
image forming sections 352, 353 and 354, visual images of magenta toner,
cyan toner and black toner are superimposed on the intermediate transfer
belt 355, a color image formed on the intermediate transfer belt is
transferred onto a recording medium 326, and a toner remaining on the
intermediate transfer belt 355 was removed by an intermediate transfer
belt cleaning unit 358. The color image forming on the recording medium
326 is fixed by the fixing unit 327.

Comparative Example 17

Image Formation and Evaluation

[0557]A two-component developer was prepared using Toner 11 in the same
manner as in Example 17, the image forming apparatus (evaluation system
B) shown in FIG. 21 was filled with the two-component developer, and
various physical properties of the toner were evaluated in the same
manner as in Example 17. Table 8 shows the evaluation results.

[0558]The toner of the present invention is excellent in all the
properties of low-temperature fixing property, offset resistance, storage
stability, charge rising property, charge stability with time and
pulverizability and can be suitably used in electrophotographic image
forming apparatuses, electrophotographic image forming methods,
developers, toner containers and process cartridges.

[0559]Because the image forming apparatus, the image forming method and
the process cartridge of the present invention respectively use the toner
of the present invention and allow for forming extremely high-quality
images over a long period of time without substantially causing a change
in color tone and abnormal images such as reduction in image density and
background smear, they can be widely used in, for example, laser
printers, direct digital photoengraving machines, full-color copiers
based on a direct or indirect electrophotographic multi-color image
developing method, full-color laser printers and full-color regular paper
facsimiles and the like.